text: // Copyright 2013 the V8 project authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #include "src/profiler/heap-snapshot-generator.h"
  
  #include <utility>
  
  #include "src/api/api-inl.h"
  #include "src/codegen/assembler-inl.h"
  #include "src/common/globals.h"
  #include "src/debug/debug.h"
  #include "src/handles/global-handles.h"
  #include "src/heap/combined-heap.h"
  #include "src/heap/safepoint.h"
  #include "src/numbers/conversions.h"
  #include "src/objects/allocation-site-inl.h"
  #include "src/objects/api-callbacks.h"
  #include "src/objects/cell-inl.h"
  #include "src/objects/feedback-cell-inl.h"
  #include "src/objects/hash-table-inl.h"
  #include "src/objects/js-array-buffer-inl.h"
  #include "src/objects/js-array-inl.h"
  #include "src/objects/js-collection-inl.h"
  #include "src/objects/js-generator-inl.h"
  #include "src/objects/js-promise-inl.h"
  #include "src/objects/js-regexp-inl.h"
  #include "src/objects/layout-descriptor.h"
  #include "src/objects/literal-objects-inl.h"
  #include "src/objects/objects-body-descriptors.h"
  #include "src/objects/objects-inl.h"
  #include "src/objects/prototype.h"
  #include "src/objects/slots-inl.h"
  #include "src/objects/struct-inl.h"
  #include "src/objects/transitions-inl.h"
  #include "src/objects/visitors.h"
  #include "src/profiler/allocation-tracker.h"
  #include "src/profiler/heap-profiler.h"
  #include "src/profiler/heap-snapshot-generator-inl.h"
  #include "src/utils/vector.h"
  
  namespace v8 {
  namespace internal {
  
  HeapGraphEdge::HeapGraphEdge(Type type, const char* name, HeapEntry* from,
                               HeapEntry* to)
      : bit_field_(TypeField::encode(type) |
                   FromIndexField::encode(from->index())),
        to_entry_(to),
        name_(name) {
    DCHECK(type == kContextVariable
        || type == kProperty
        || type == kInternal
        || type == kShortcut
        || type == kWeak);
  }
  
  HeapGraphEdge::HeapGraphEdge(Type type, int index, HeapEntry* from,
                               HeapEntry* to)
      : bit_field_(TypeField::encode(type) |
                   FromIndexField::encode(from->index())),
        to_entry_(to),
        index_(index) {
    DCHECK(type == kElement || type == kHidden);
  }
  
  HeapEntry::HeapEntry(HeapSnapshot* snapshot, int index, Type type,
                       const char* name, SnapshotObjectId id, size_t self_size,
                       unsigned trace_node_id)
      : type_(type),
        index_(index),
        children_count_(0),
        self_size_(self_size),
        snapshot_(snapshot),
        name_(name),
        id_(id),
        trace_node_id_(trace_node_id) {
    DCHECK_GE(index, 0);
  }
  
  void HeapEntry::SetNamedReference(HeapGraphEdge::Type type,
                                    const char* name,
                                    HeapEntry* entry) {
    ++children_count_;
    snapshot_->edges().emplace_back(type, name, this, entry);
  }
  
  void HeapEntry::SetIndexedReference(HeapGraphEdge::Type type,
                                      int index,
                                      HeapEntry* entry) {
    ++children_count_;
    snapshot_->edges().emplace_back(type, index, this, entry);
  }
  
  void HeapEntry::SetNamedAutoIndexReference(HeapGraphEdge::Type type,
                                             const char* description,
                                             HeapEntry* child,
                                             StringsStorage* names) {
    int index = children_count_ + 1;
    const char* name = description
                           ? names->GetFormatted("%d / %s", index, description)
                           : names->GetName(index);
    SetNamedReference(type, name, child);
  }
  
  void HeapEntry::Print(
      const char* prefix, const char* edge_name, int max_depth, int indent) {
    STATIC_ASSERT(sizeof(unsigned) == sizeof(id()));
    base::OS::Print("%6zu @%6u %*c %s%s: ", self_size(), id(), indent, ' ',
                    prefix, edge_name);
    if (type() != kString) {
      base::OS::Print("%s %.40s\n", TypeAsString(), name_);
    } else {
      base::OS::Print("\"");
      const char* c = name_;
      while (*c && (c - name_) <= 40) {
        if (*c != '\n')
          base::OS::Print("%c", *c);
        else
          base::OS::Print("\\n");
        ++c;
      }
      base::OS::Print("\"\n");
    }
    if (--max_depth == 0) return;
    for (auto i = children_begin(); i != children_end(); ++i) {
      HeapGraphEdge& edge = **i;
      const char* edge_prefix = "";
      EmbeddedVector<char, 64> index;
      const char* edge_name = index.begin();
      switch (edge.type()) {
        case HeapGraphEdge::kContextVariable:
          edge_prefix = "#";
          edge_name = edge.name();
          break;
        case HeapGraphEdge::kElement:
          SNPrintF(index, "%d", edge.index());
          break;
        case HeapGraphEdge::kInternal:
          edge_prefix = "$";
          edge_name = edge.name();
          break;
        case HeapGraphEdge::kProperty:
          edge_name = edge.name();
          break;
        case HeapGraphEdge::kHidden:
          edge_prefix = "$";
          SNPrintF(index, "%d", edge.index());
          break;
        case HeapGraphEdge::kShortcut:
          edge_prefix = "^";
          edge_name = edge.name();
          break;
        case HeapGraphEdge::kWeak:
          edge_prefix = "w";
          edge_name = edge.name();
          break;
        default:
          SNPrintF(index, "!!! unknown edge type: %d ", edge.type());
      }
      edge.to()->Print(edge_prefix, edge_name, max_depth, indent + 2);
    }
  }
  
  const char* HeapEntry::TypeAsString() {
    switch (type()) {
      case kHidden: return "/hidden/";
      case kObject: return "/object/";
      case kClosure: return "/closure/";
      case kString: return "/string/";
      case kCode: return "/code/";
      case kArray: return "/array/";
      case kRegExp: return "/regexp/";
      case kHeapNumber: return "/number/";
      case kNative: return "/native/";
      case kSynthetic: return "/synthetic/";
      case kConsString: return "/concatenated string/";
      case kSlicedString: return "/sliced string/";
      case kSymbol: return "/symbol/";
      case kBigInt:
        return "/bigint/";
      default: return "???";
    }
  }
  
  HeapSnapshot::HeapSnapshot(HeapProfiler* profiler, bool global_objects_as_roots)
      : profiler_(profiler),
        treat_global_objects_as_roots_(global_objects_as_roots) {
    // It is very important to keep objects that form a heap snapshot
    // as small as possible. Check assumptions about data structure sizes.
    STATIC_ASSERT(kSystemPointerSize != 4 || sizeof(HeapGraphEdge) == 12);
    STATIC_ASSERT(kSystemPointerSize != 8 || sizeof(HeapGraphEdge) == 24);
    STATIC_ASSERT(kSystemPointerSize != 4 || sizeof(HeapEntry) == 32);
  #if V8_CC_MSVC
    STATIC_ASSERT(kSystemPointerSize != 8 || sizeof(HeapEntry) == 48);
  #else   // !V8_CC_MSVC
    STATIC_ASSERT(kSystemPointerSize != 8 || sizeof(HeapEntry) == 40);
  #endif  // !V8_CC_MSVC
    memset(&gc_subroot_entries_, 0, sizeof(gc_subroot_entries_));
  }
  
  void HeapSnapshot::Delete() {
    profiler_->RemoveSnapshot(this);
  }
  
  void HeapSnapshot::RememberLastJSObjectId() {
    max_snapshot_js_object_id_ = profiler_->heap_object_map()->last_assigned_id();
  }
  
  void HeapSnapshot::AddSyntheticRootEntries() {
    AddRootEntry();
    AddGcRootsEntry();
    SnapshotObjectId id = HeapObjectsMap::kGcRootsFirstSubrootId;
    for (int root = 0; root < static_cast<int>(Root::kNumberOfRoots); root++) {
      AddGcSubrootEntry(static_cast<Root>(root), id);
      id += HeapObjectsMap::kObjectIdStep;
    }
    DCHECK_EQ(HeapObjectsMap::kFirstAvailableObjectId, id);
  }
  
  void HeapSnapshot::AddRootEntry() {
    DCHECK_NULL(root_entry_);
    DCHECK(entries_.empty());  // Root entry must be the first one.
    root_entry_ = AddEntry(HeapEntry::kSynthetic, "",
                           HeapObjectsMap::kInternalRootObjectId, 0, 0);
    DCHECK_EQ(1u, entries_.size());
    DCHECK_EQ(root_entry_, &entries_.front());
  }
  
  void HeapSnapshot::AddGcRootsEntry() {
    DCHECK_NULL(gc_roots_entry_);
    gc_roots_entry_ = AddEntry(HeapEntry::kSynthetic, "(GC roots)",
                               HeapObjectsMap::kGcRootsObjectId, 0, 0);
  }
  
  void HeapSnapshot::AddGcSubrootEntry(Root root, SnapshotObjectId id) {
    DCHECK_NULL(gc_subroot_entries_[static_cast<int>(root)]);
    gc_subroot_entries_[static_cast<int>(root)] =
        AddEntry(HeapEntry::kSynthetic, RootVisitor::RootName(root), id, 0, 0);
  }
  
  void HeapSnapshot::AddLocation(HeapEntry* entry, int scriptId, int line,
                                 int col) {
    locations_.emplace_back(entry->index(), scriptId, line, col);
  }
  
  HeapEntry* HeapSnapshot::AddEntry(HeapEntry::Type type,
                                    const char* name,
                                    SnapshotObjectId id,
                                    size_t size,
                                    unsigned trace_node_id) {
    DCHECK(!is_complete());
    entries_.emplace_back(this, static_cast<int>(entries_.size()), type, name, id,
                          size, trace_node_id);
    return &entries_.back();
  }
  
  void HeapSnapshot::FillChildren() {
    DCHECK(children().empty());
    int children_index = 0;
    for (HeapEntry& entry : entries()) {
      children_index = entry.set_children_index(children_index);
    }
    DCHECK_EQ(edges().size(), static_cast<size_t>(children_index));
    children().resize(edges().size());
    for (HeapGraphEdge& edge : edges()) {
      edge.from()->add_child(&edge);
    }
  }
  
  HeapEntry* HeapSnapshot::GetEntryById(SnapshotObjectId id) {
    if (entries_by_id_cache_.empty()) {
      CHECK(is_complete());
      entries_by_id_cache_.reserve(entries_.size());
      for (HeapEntry& entry : entries_) {
        entries_by_id_cache_.emplace(entry.id(), &entry);
      }
    }
    auto it = entries_by_id_cache_.find(id);
    return it != entries_by_id_cache_.end() ? it->second : nullptr;
  }
  
  void HeapSnapshot::Print(int max_depth) {
    root()->Print("", "", max_depth, 0);
  }
  
  // We split IDs on evens for embedder objects (see
  // HeapObjectsMap::GenerateId) and odds for native objects.
  const SnapshotObjectId HeapObjectsMap::kInternalRootObjectId = 1;
  const SnapshotObjectId HeapObjectsMap::kGcRootsObjectId =
      HeapObjectsMap::kInternalRootObjectId + HeapObjectsMap::kObjectIdStep;
  const SnapshotObjectId HeapObjectsMap::kGcRootsFirstSubrootId =
      HeapObjectsMap::kGcRootsObjectId + HeapObjectsMap::kObjectIdStep;
  const SnapshotObjectId HeapObjectsMap::kFirstAvailableObjectId =
      HeapObjectsMap::kGcRootsFirstSubrootId +
      static_cast<int>(Root::kNumberOfRoots) * HeapObjectsMap::kObjectIdStep;
  
  HeapObjectsMap::HeapObjectsMap(Heap* heap)
      : next_id_(kFirstAvailableObjectId), heap_(heap) {
    // The dummy element at zero index is needed as entries_map_ cannot hold
    // an entry with zero value. Otherwise it's impossible to tell if
    // LookupOrInsert has added a new item or just returning exisiting one
    // having the value of zero.
    entries_.emplace_back(0, kNullAddress, 0, true);
  }
  
  bool HeapObjectsMap::MoveObject(Address from, Address to, int object_size) {
    DCHECK_NE(kNullAddress, to);
    DCHECK_NE(kNullAddress, from);
    if (from == to) return false;
    void* from_value = entries_map_.Remove(reinterpret_cast<void*>(from),
                                           ComputeAddressHash(from));
    if (from_value == nullptr) {
      // It may occur that some untracked object moves to an address X and there
      // is a tracked object at that address. In this case we should remove the
      // entry as we know that the object has died.
      void* to_value = entries_map_.Remove(reinterpret_cast<void*>(to),
                                           ComputeAddressHash(to));
      if (to_value != nullptr) {
        int to_entry_info_index =
            static_cast<int>(reinterpret_cast<intptr_t>(to_value));
        entries_.at(to_entry_info_index).addr = kNullAddress;
      }
    } else {
      base::HashMap::Entry* to_entry = entries_map_.LookupOrInsert(
          reinterpret_cast<void*>(to), ComputeAddressHash(to));
      if (to_entry->value != nullptr) {
        // We found the existing entry with to address for an old object.
        // Without this operation we will have two EntryInfo's with the same
        // value in addr field. It is bad because later at RemoveDeadEntries
        // one of this entry will be removed with the corresponding entries_map_
        // entry.
        int to_entry_info_index =
            static_cast<int>(reinterpret_cast<intptr_t>(to_entry->value));
        entries_.at(to_entry_info_index).addr = kNullAddress;
      }
      int from_entry_info_index =
          static_cast<int>(reinterpret_cast<intptr_t>(from_value));
      entries_.at(from_entry_info_index).addr = to;
      // Size of an object can change during its life, so to keep information
      // about the object in entries_ consistent, we have to adjust size when the
      // object is migrated.
      if (FLAG_heap_profiler_trace_objects) {
        PrintF("Move object from %p to %p old size %6d new size %6d\n",
               reinterpret_cast<void*>(from), reinterpret_cast<void*>(to),
               entries_.at(from_entry_info_index).size, object_size);
      }
      entries_.at(from_entry_info_index).size = object_size;
      to_entry->value = from_value;
    }
    return from_value != nullptr;
  }
  
  
  void HeapObjectsMap::UpdateObjectSize(Address addr, int size) {
    FindOrAddEntry(addr, size, false);
  }
  
  
  SnapshotObjectId HeapObjectsMap::FindEntry(Address addr) {
    base::HashMap::Entry* entry = entries_map_.Lookup(
        reinterpret_cast<void*>(addr), ComputeAddressHash(addr));
    if (entry == nullptr) return v8::HeapProfiler::kUnknownObjectId;
    int entry_index = static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
    EntryInfo& entry_info = entries_.at(entry_index);
    DCHECK(static_cast<uint32_t>(entries_.size()) > entries_map_.occupancy());
    return entry_info.id;
  }
  
  
  SnapshotObjectId HeapObjectsMap::FindOrAddEntry(Address addr,
                                                  unsigned int size,
                                                  bool accessed) {
    DCHECK(static_cast<uint32_t>(entries_.size()) > entries_map_.occupancy());
    base::HashMap::Entry* entry = entries_map_.LookupOrInsert(
        reinterpret_cast<void*>(addr), ComputeAddressHash(addr));
    if (entry->value != nullptr) {
      int entry_index =
          static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
      EntryInfo& entry_info = entries_.at(entry_index);
      entry_info.accessed = accessed;
      if (FLAG_heap_profiler_trace_objects) {
        PrintF("Update object size : %p with old size %d and new size %d\n",
               reinterpret_cast<void*>(addr), entry_info.size, size);
      }
      entry_info.size = size;
      return entry_info.id;
    }
    entry->value = reinterpret_cast<void*>(entries_.size());
    SnapshotObjectId id = next_id_;
    next_id_ += kObjectIdStep;
    entries_.push_back(EntryInfo(id, addr, size, accessed));
    DCHECK(static_cast<uint32_t>(entries_.size()) > entries_map_.occupancy());
    return id;
  }
  
  SnapshotObjectId HeapObjectsMap::FindMergedNativeEntry(NativeObject addr) {
    auto it = merged_native_entries_map_.find(addr);
    if (it == merged_native_entries_map_.end())
      return v8::HeapProfiler::kUnknownObjectId;
    return entries_[it->second].id;
  }
  
  void HeapObjectsMap::AddMergedNativeEntry(NativeObject addr,
                                            Address canonical_addr) {
    base::HashMap::Entry* entry =
        entries_map_.Lookup(reinterpret_cast<void*>(canonical_addr),
                            ComputeAddressHash(canonical_addr));
    auto result = merged_native_entries_map_.insert(
        {addr, reinterpret_cast<size_t>(entry->value)});
    if (!result.second) {
      result.first->second = reinterpret_cast<size_t>(entry->value);
    }
  }
  
  void HeapObjectsMap::StopHeapObjectsTracking() { time_intervals_.clear(); }
  
  void HeapObjectsMap::UpdateHeapObjectsMap() {
    if (FLAG_heap_profiler_trace_objects) {
      PrintF("Begin HeapObjectsMap::UpdateHeapObjectsMap. map has %d entries.\n",
             entries_map_.occupancy());
    }
    heap_->PreciseCollectAllGarbage(Heap::kNoGCFlags,
                                    GarbageCollectionReason::kHeapProfiler);
    CombinedHeapObjectIterator iterator(heap_);
    for (HeapObject obj = iterator.Next(); !obj.is_null();
         obj = iterator.Next()) {
      FindOrAddEntry(obj.address(), obj.Size());
      if (FLAG_heap_profiler_trace_objects) {
        PrintF("Update object      : %p %6d. Next address is %p\n",
               reinterpret_cast<void*>(obj.address()), obj.Size(),
               reinterpret_cast<void*>(obj.address() + obj.Size()));
      }
    }
    RemoveDeadEntries();
    if (FLAG_heap_profiler_trace_objects) {
      PrintF("End HeapObjectsMap::UpdateHeapObjectsMap. map has %d entries.\n",
             entries_map_.occupancy());
    }
  }
  
  SnapshotObjectId HeapObjectsMap::PushHeapObjectsStats(OutputStream* stream,
                                                        int64_t* timestamp_us) {
    UpdateHeapObjectsMap();
    time_intervals_.emplace_back(next_id_);
    int prefered_chunk_size = stream->GetChunkSize();
    std::vector<v8::HeapStatsUpdate> stats_buffer;
    DCHECK(!entries_.empty());
    EntryInfo* entry_info = &entries_.front();
    EntryInfo* end_entry_info = &entries_.back() + 1;
    for (size_t time_interval_index = 0;
         time_interval_index < time_intervals_.size(); ++time_interval_index) {
      TimeInterval& time_interval = time_intervals_[time_interval_index];
      SnapshotObjectId time_interval_id = time_interval.id;
      uint32_t entries_size = 0;
      EntryInfo* start_entry_info = entry_info;
      while (entry_info < end_entry_info && entry_info->id < time_interval_id) {
        entries_size += entry_info->size;
        ++entry_info;
      }
      uint32_t entries_count =
          static_cast<uint32_t>(entry_info - start_entry_info);
      if (time_interval.count != entries_count ||
          time_interval.size != entries_size) {
        stats_buffer.emplace_back(static_cast<uint32_t>(time_interval_index),
                                  time_interval.count = entries_count,
                                  time_interval.size = entries_size);
        if (static_cast<int>(stats_buffer.size()) >= prefered_chunk_size) {
          OutputStream::WriteResult result = stream->WriteHeapStatsChunk(
              &stats_buffer.front(), static_cast<int>(stats_buffer.size()));
          if (result == OutputStream::kAbort) return last_assigned_id();
          stats_buffer.clear();
        }
      }
    }
    DCHECK(entry_info == end_entry_info);
    if (!stats_buffer.empty()) {
      OutputStream::WriteResult result = stream->WriteHeapStatsChunk(
          &stats_buffer.front(), static_cast<int>(stats_buffer.size()));
      if (result == OutputStream::kAbort) return last_assigned_id();
    }
    stream->EndOfStream();
    if (timestamp_us) {
      *timestamp_us =
          (time_intervals_.back().timestamp - time_intervals_.front().timestamp)
              .InMicroseconds();
    }
    return last_assigned_id();
  }
  
  
  void HeapObjectsMap::RemoveDeadEntries() {
    DCHECK(entries_.size() > 0 && entries_.at(0).id == 0 &&
           entries_.at(0).addr == kNullAddress);
  
    // Build up temporary reverse map.
    std::unordered_map<size_t, NativeObject> reverse_merged_native_entries_map;
    for (const auto& it : merged_native_entries_map_) {
      auto result =
          reverse_merged_native_entries_map.emplace(it.second, it.first);
      DCHECK(result.second);
      USE(result);
    }
  
    size_t first_free_entry = 1;
    for (size_t i = 1; i < entries_.size(); ++i) {
      EntryInfo& entry_info = entries_.at(i);
      auto merged_reverse_it = reverse_merged_native_entries_map.find(i);
      if (entry_info.accessed) {
        if (first_free_entry != i) {
          entries_.at(first_free_entry) = entry_info;
        }
        entries_.at(first_free_entry).accessed = false;
        base::HashMap::Entry* entry =
            entries_map_.Lookup(reinterpret_cast<void*>(entry_info.addr),
                                ComputeAddressHash(entry_info.addr));
        DCHECK(entry);
        entry->value = reinterpret_cast<void*>(first_free_entry);
        if (merged_reverse_it != reverse_merged_native_entries_map.end()) {
          auto it = merged_native_entries_map_.find(merged_reverse_it->second);
          DCHECK_NE(merged_native_entries_map_.end(), it);
          it->second = first_free_entry;
        }
        ++first_free_entry;
      } else {
        if (entry_info.addr) {
          entries_map_.Remove(reinterpret_cast<void*>(entry_info.addr),
                              ComputeAddressHash(entry_info.addr));
          if (merged_reverse_it != reverse_merged_native_entries_map.end()) {
            merged_native_entries_map_.erase(merged_reverse_it->second);
          }
        }
      }
    }
    entries_.erase(entries_.begin() + first_free_entry, entries_.end());
  
    DCHECK(static_cast<uint32_t>(entries_.size()) - 1 ==
           entries_map_.occupancy());
  }
  
  V8HeapExplorer::V8HeapExplorer(HeapSnapshot* snapshot,
                                 SnapshottingProgressReportingInterface* progress,
                                 v8::HeapProfiler::ObjectNameResolver* resolver)
      : heap_(snapshot->profiler()->heap_object_map()->heap()),
        snapshot_(snapshot),
        names_(snapshot_->profiler()->names()),
        heap_object_map_(snapshot_->profiler()->heap_object_map()),
        progress_(progress),
        generator_(nullptr),
        global_object_name_resolver_(resolver) {}
  
  HeapEntry* V8HeapExplorer::AllocateEntry(HeapThing ptr) {
    return AddEntry(HeapObject::cast(Object(reinterpret_cast<Address>(ptr))));
  }
  
  void V8HeapExplorer::ExtractLocation(HeapEntry* entry, HeapObject object) {
    if (object.IsJSFunction()) {
      JSFunction func = JSFunction::cast(object);
      ExtractLocationForJSFunction(entry, func);
  
    } else if (object.IsJSGeneratorObject()) {
      JSGeneratorObject gen = JSGeneratorObject::cast(object);
      ExtractLocationForJSFunction(entry, gen.function());
  
    } else if (object.IsJSObject()) {
      JSObject obj = JSObject::cast(object);
      JSFunction maybe_constructor = GetConstructor(obj);
  
      if (!maybe_constructor.is_null()) {
        ExtractLocationForJSFunction(entry, maybe_constructor);
      }
    }
  }
  
  void V8HeapExplorer::ExtractLocationForJSFunction(HeapEntry* entry,
                                                    JSFunction func) {
    if (!func.shared().script().IsScript()) return;
    Script script = Script::cast(func.shared().script());
    int scriptId = script.id();
    int start = func.shared().StartPosition();
    int line = script.GetLineNumber(start);
    int col = script.GetColumnNumber(start);
    snapshot_->AddLocation(entry, scriptId, line, col);
  }
  
  HeapEntry* V8HeapExplorer::AddEntry(HeapObject object) {
    if (object.IsJSFunction()) {
      JSFunction func = JSFunction::cast(object);
      SharedFunctionInfo shared = func.shared();
      const char* name = names_->GetName(shared.Name());
      return AddEntry(object, HeapEntry::kClosure, name);
    } else if (object.IsJSBoundFunction()) {
      return AddEntry(object, HeapEntry::kClosure, "native_bind");
    } else if (object.IsJSRegExp()) {
      JSRegExp re = JSRegExp::cast(object);
      return AddEntry(object, HeapEntry::kRegExp, names_->GetName(re.Pattern()));
    } else if (object.IsJSObject()) {
      const char* name = names_->GetName(
          GetConstructorName(JSObject::cast(object)));
      if (object.IsJSGlobalObject()) {
        auto it = objects_tags_.find(JSGlobalObject::cast(object));
        if (it != objects_tags_.end()) {
          name = names_->GetFormatted("%s / %s", name, it->second);
        }
      }
      return AddEntry(object, HeapEntry::kObject, name);
    } else if (object.IsString()) {
      String string = String::cast(object);
      if (string.IsConsString()) {
        return AddEntry(object, HeapEntry::kConsString, "(concatenated string)");
      } else if (string.IsSlicedString()) {
        return AddEntry(object, HeapEntry::kSlicedString, "(sliced string)");
      } else {
        return AddEntry(object, HeapEntry::kString,
                        names_->GetName(String::cast(object)));
      }
    } else if (object.IsSymbol()) {
      if (Symbol::cast(object).is_private())
        return AddEntry(object, HeapEntry::kHidden, "private symbol");
      else
        return AddEntry(object, HeapEntry::kSymbol, "symbol");
    } else if (object.IsBigInt()) {
      return AddEntry(object, HeapEntry::kBigInt, "bigint");
    } else if (object.IsCode()) {
      return AddEntry(object, HeapEntry::kCode, "");
    } else if (object.IsSharedFunctionInfo()) {
      String name = SharedFunctionInfo::cast(object).Name();
      return AddEntry(object, HeapEntry::kCode, names_->GetName(name));
    } else if (object.IsScript()) {
      Object name = Script::cast(object).name();
      return AddEntry(object, HeapEntry::kCode,
                      name.IsString() ? names_->GetName(String::cast(name)) : "");
    } else if (object.IsNativeContext()) {
      return AddEntry(object, HeapEntry::kHidden, "system / NativeContext");
    } else if (object.IsContext()) {
      return AddEntry(object, HeapEntry::kObject, "system / Context");
    } else if (object.IsFixedArray() || object.IsFixedDoubleArray() ||
               object.IsByteArray()) {
      return AddEntry(object, HeapEntry::kArray, "");
    } else if (object.IsHeapNumber()) {
      return AddEntry(object, HeapEntry::kHeapNumber, "number");
    }
    return AddEntry(object, HeapEntry::kHidden, GetSystemEntryName(object));
  }
  
  HeapEntry* V8HeapExplorer::AddEntry(HeapObject object, HeapEntry::Type type,
                                      const char* name) {
    return AddEntry(object.address(), type, name, object.Size());
  }
  
  HeapEntry* V8HeapExplorer::AddEntry(Address address,
                                      HeapEntry::Type type,
                                      const char* name,
                                      size_t size) {
    SnapshotObjectId object_id = heap_object_map_->FindOrAddEntry(
        address, static_cast<unsigned int>(size));
    unsigned trace_node_id = 0;
    if (AllocationTracker* allocation_tracker =
        snapshot_->profiler()->allocation_tracker()) {
      trace_node_id =
          allocation_tracker->address_to_trace()->GetTraceNodeId(address);
    }
    return snapshot_->AddEntry(type, name, object_id, size, trace_node_id);
  }
  
  const char* V8HeapExplorer::GetSystemEntryName(HeapObject object) {
    switch (object.map().instance_type()) {
      case MAP_TYPE:
        switch (Map::cast(object).instance_type()) {
  #define MAKE_STRING_MAP_CASE(instance_type, size, name, Name) \
          case instance_type: return "system / Map (" #Name ")";
        STRING_TYPE_LIST(MAKE_STRING_MAP_CASE)
  #undef MAKE_STRING_MAP_CASE
          default: return "system / Map";
        }
      case CELL_TYPE: return "system / Cell";
      case PROPERTY_CELL_TYPE: return "system / PropertyCell";
      case FOREIGN_TYPE: return "system / Foreign";
      case ODDBALL_TYPE: return "system / Oddball";
      case ALLOCATION_SITE_TYPE:
        return "system / AllocationSite";
  #define MAKE_STRUCT_CASE(TYPE, Name, name) \
    case TYPE:                               \
      return "system / " #Name;
        STRUCT_LIST(MAKE_STRUCT_CASE)
  #undef MAKE_STRUCT_CASE
      default: return "system";
    }
  }
  
  int V8HeapExplorer::EstimateObjectsCount() {
    CombinedHeapObjectIterator it(heap_, HeapObjectIterator::kFilterUnreachable);
    int objects_count = 0;
    while (!it.Next().is_null()) ++objects_count;
    return objects_count;
  }
  
  class IndexedReferencesExtractor : public ObjectVisitor {
   public:
    IndexedReferencesExtractor(V8HeapExplorer* generator, HeapObject parent_obj,
                               HeapEntry* parent)
        : generator_(generator),
          parent_obj_(parent_obj),
          parent_start_(parent_obj_.RawMaybeWeakField(0)),
          parent_end_(parent_obj_.RawMaybeWeakField(parent_obj_.Size())),
          parent_(parent),
          next_index_(0) {}
    void VisitPointers(HeapObject host, ObjectSlot start,
                       ObjectSlot end) override {
      VisitPointers(host, MaybeObjectSlot(start), MaybeObjectSlot(end));
    }
    void VisitPointers(HeapObject host, MaybeObjectSlot start,
                       MaybeObjectSlot end) override {
      // [start,end) must be a sub-region of [parent_start_, parent_end), i.e.
      // all the slots must point inside the object.
      CHECK_LE(parent_start_, start);
      CHECK_LE(end, parent_end_);
      for (MaybeObjectSlot p = start; p < end; ++p) {
        int field_index = static_cast<int>(p - parent_start_);
        if (generator_->visited_fields_[field_index]) {
          generator_->visited_fields_[field_index] = false;
          continue;
        }
        HeapObject heap_object;
        if ((*p)->GetHeapObject(&heap_object)) {
          VisitHeapObjectImpl(heap_object, field_index);
        }
      }
    }
  
    void VisitCodeTarget(Code host, RelocInfo* rinfo) override {
      Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
      VisitHeapObjectImpl(target, -1);
    }
  
    void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
      VisitHeapObjectImpl(rinfo->target_object(), -1);
    }
  
   private:
    V8_INLINE void VisitHeapObjectImpl(HeapObject heap_object, int field_index) {
      DCHECK_LE(-1, field_index);
      // The last parameter {field_offset} is only used to check some well-known
      // skipped references, so passing -1 * kTaggedSize for objects embedded
      // into code is fine.
      generator_->SetHiddenReference(parent_obj_, parent_, next_index_++,
                                     heap_object, field_index * kTaggedSize);
    }
  
    V8HeapExplorer* generator_;
    HeapObject parent_obj_;
    MaybeObjectSlot parent_start_;
    MaybeObjectSlot parent_end_;
    HeapEntry* parent_;
    int next_index_;
  };
  
  void V8HeapExplorer::ExtractReferences(HeapEntry* entry, HeapObject obj) {
    if (obj.IsJSGlobalProxy()) {
      ExtractJSGlobalProxyReferences(entry, JSGlobalProxy::cast(obj));
    } else if (obj.IsJSArrayBuffer()) {
      ExtractJSArrayBufferReferences(entry, JSArrayBuffer::cast(obj));
    } else if (obj.IsJSObject()) {
      if (obj.IsJSWeakSet()) {
        ExtractJSWeakCollectionReferences(entry, JSWeakSet::cast(obj));
      } else if (obj.IsJSWeakMap()) {
        ExtractJSWeakCollectionReferences(entry, JSWeakMap::cast(obj));
      } else if (obj.IsJSSet()) {
        ExtractJSCollectionReferences(entry, JSSet::cast(obj));
      } else if (obj.IsJSMap()) {
        ExtractJSCollectionReferences(entry, JSMap::cast(obj));
      } else if (obj.IsJSPromise()) {
        ExtractJSPromiseReferences(entry, JSPromise::cast(obj));
      } else if (obj.IsJSGeneratorObject()) {
        ExtractJSGeneratorObjectReferences(entry, JSGeneratorObject::cast(obj));
      }
      ExtractJSObjectReferences(entry, JSObject::cast(obj));
    } else if (obj.IsString()) {
      ExtractStringReferences(entry, String::cast(obj));
    } else if (obj.IsSymbol()) {
      ExtractSymbolReferences(entry, Symbol::cast(obj));
    } else if (obj.IsMap()) {
      ExtractMapReferences(entry, Map::cast(obj));
    } else if (obj.IsSharedFunctionInfo()) {
      ExtractSharedFunctionInfoReferences(entry, SharedFunctionInfo::cast(obj));
    } else if (obj.IsScript()) {
      ExtractScriptReferences(entry, Script::cast(obj));
    } else if (obj.IsAccessorInfo()) {
      ExtractAccessorInfoReferences(entry, AccessorInfo::cast(obj));
    } else if (obj.IsAccessorPair()) {
      ExtractAccessorPairReferences(entry, AccessorPair::cast(obj));
    } else if (obj.IsCode()) {
      ExtractCodeReferences(entry, Code::cast(obj));
    } else if (obj.IsCell()) {
      ExtractCellReferences(entry, Cell::cast(obj));
    } else if (obj.IsFeedbackCell()) {
      ExtractFeedbackCellReferences(entry, FeedbackCell::cast(obj));
    } else if (obj.IsPropertyCell()) {
      ExtractPropertyCellReferences(entry, PropertyCell::cast(obj));
    } else if (obj.IsAllocationSite()) {
      ExtractAllocationSiteReferences(entry, AllocationSite::cast(obj));
    } else if (obj.IsArrayBoilerplateDescription()) {
      ExtractArrayBoilerplateDescriptionReferences(
          entry, ArrayBoilerplateDescription::cast(obj));
    } else if (obj.IsFeedbackVector()) {
      ExtractFeedbackVectorReferences(entry, FeedbackVector::cast(obj));
    } else if (obj.IsDescriptorArray()) {
      ExtractDescriptorArrayReferences(entry, DescriptorArray::cast(obj));
    } else if (obj.IsWeakFixedArray()) {
      ExtractWeakArrayReferences(WeakFixedArray::kHeaderSize, entry,
                                 WeakFixedArray::cast(obj));
    } else if (obj.IsWeakArrayList()) {
      ExtractWeakArrayReferences(WeakArrayList::kHeaderSize, entry,
                                 WeakArrayList::cast(obj));
    } else if (obj.IsContext()) {
      ExtractContextReferences(entry, Context::cast(obj));
    } else if (obj.IsEphemeronHashTable()) {
      ExtractEphemeronHashTableReferences(entry, EphemeronHashTable::cast(obj));
    } else if (obj.IsFixedArray()) {
      ExtractFixedArrayReferences(entry, FixedArray::cast(obj));
    }
  }
  
  void V8HeapExplorer::ExtractJSGlobalProxyReferences(HeapEntry* entry,
                                                      JSGlobalProxy proxy) {
    SetInternalReference(entry, "native_context", proxy.native_context(),
                         JSGlobalProxy::kNativeContextOffset);
  }
  
  void V8HeapExplorer::ExtractJSObjectReferences(HeapEntry* entry,
                                                 JSObject js_obj) {
    HeapObject obj = js_obj;
    ExtractPropertyReferences(js_obj, entry);
    ExtractElementReferences(js_obj, entry);
    ExtractInternalReferences(js_obj, entry);
    Isolate* isolate = Isolate::FromHeap(heap_);
    PrototypeIterator iter(isolate, js_obj);
    ReadOnlyRoots roots(isolate);
    SetPropertyReference(entry, roots.proto_string(), iter.GetCurrent());
    if (obj.IsJSBoundFunction()) {
      JSBoundFunction js_fun = JSBoundFunction::cast(obj);
      TagObject(js_fun.bound_arguments(), "(bound arguments)");
      SetInternalReference(entry, "bindings", js_fun.bound_arguments(),
                           JSBoundFunction::kBoundArgumentsOffset);
      SetInternalReference(entry, "bound_this", js_fun.bound_this(),
                           JSBoundFunction::kBoundThisOffset);
      SetInternalReference(entry, "bound_function",
                           js_fun.bound_target_function(),
                           JSBoundFunction::kBoundTargetFunctionOffset);
      FixedArray bindings = js_fun.bound_arguments();
      for (int i = 0; i < bindings.length(); i++) {
        const char* reference_name = names_->GetFormatted("bound_argument_%d", i);
        SetNativeBindReference(entry, reference_name, bindings.get(i));
      }
    } else if (obj.IsJSFunction()) {
      JSFunction js_fun = JSFunction::cast(js_obj);
      if (js_fun.has_prototype_slot()) {
        Object proto_or_map = js_fun.prototype_or_initial_map();
        if (!proto_or_map.IsTheHole(isolate)) {
          if (!proto_or_map.IsMap()) {
            SetPropertyReference(entry, roots.prototype_string(), proto_or_map,
                                 nullptr,
                                 JSFunction::kPrototypeOrInitialMapOffset);
          } else {
            SetPropertyReference(entry, roots.prototype_string(),
                                 js_fun.prototype());
            SetInternalReference(entry, "initial_map", proto_or_map,
                                 JSFunction::kPrototypeOrInitialMapOffset);
          }
        }
      }
      SharedFunctionInfo shared_info = js_fun.shared();
      TagObject(js_fun.raw_feedback_cell(), "(function feedback cell)");
      SetInternalReference(entry, "feedback_cell", js_fun.raw_feedback_cell(),
                           JSFunction::kFeedbackCellOffset);
      TagObject(shared_info, "(shared function info)");
      SetInternalReference(entry, "shared", shared_info,
                           JSFunction::kSharedFunctionInfoOffset);
      TagObject(js_fun.context(), "(context)");
      SetInternalReference(entry, "context", js_fun.context(),
                           JSFunction::kContextOffset);
      SetInternalReference(entry, "code", js_fun.code(), JSFunction::kCodeOffset);
    } else if (obj.IsJSGlobalObject()) {
      JSGlobalObject global_obj = JSGlobalObject::cast(obj);
      SetInternalReference(entry, "native_context", global_obj.native_context(),
                           JSGlobalObject::kNativeContextOffset);
      SetInternalReference(entry, "global_proxy", global_obj.global_proxy(),
                           JSGlobalObject::kGlobalProxyOffset);
      STATIC_ASSERT(JSGlobalObject::kHeaderSize - JSObject::kHeaderSize ==
                    2 * kTaggedSize);
    } else if (obj.IsJSArrayBufferView()) {
      JSArrayBufferView view = JSArrayBufferView::cast(obj);
      SetInternalReference(entry, "buffer", view.buffer(),
                           JSArrayBufferView::kBufferOffset);
    }
  
    TagObject(js_obj.raw_properties_or_hash(), "(object properties)");
    SetInternalReference(entry, "properties", js_obj.raw_properties_or_hash(),
                         JSObject::kPropertiesOrHashOffset);
  
    TagObject(js_obj.elements(), "(object elements)");
    SetInternalReference(entry, "elements", js_obj.elements(),
                         JSObject::kElementsOffset);
  }
  
  void V8HeapExplorer::ExtractStringReferences(HeapEntry* entry, String string) {
    if (string.IsConsString()) {
      ConsString cs = ConsString::cast(string);
      SetInternalReference(entry, "first", cs.first(), ConsString::kFirstOffset);
      SetInternalReference(entry, "second", cs.second(),
                           ConsString::kSecondOffset);
    } else if (string.IsSlicedString()) {
      SlicedString ss = SlicedString::cast(string);
      SetInternalReference(entry, "parent", ss.parent(),
                           SlicedString::kParentOffset);
    } else if (string.IsThinString()) {
      ThinString ts = ThinString::cast(string);
      SetInternalReference(entry, "actual", ts.actual(),
                           ThinString::kActualOffset);
    }
  }
  
  void V8HeapExplorer::ExtractSymbolReferences(HeapEntry* entry, Symbol symbol) {
    SetInternalReference(entry, "name", symbol.description(),
                         Symbol::kDescriptionOffset);
  }
  
  void V8HeapExplorer::ExtractJSCollectionReferences(HeapEntry* entry,
                                                     JSCollection collection) {
    SetInternalReference(entry, "table", collection.table(),
                         JSCollection::kTableOffset);
  }
  
  void V8HeapExplorer::ExtractJSWeakCollectionReferences(HeapEntry* entry,
                                                         JSWeakCollection obj) {
    SetInternalReference(entry, "table", obj.table(),
                         JSWeakCollection::kTableOffset);
  }
  
  void V8HeapExplorer::ExtractEphemeronHashTableReferences(
      HeapEntry* entry, EphemeronHashTable table) {
    for (InternalIndex i : table.IterateEntries()) {
      int key_index = EphemeronHashTable::EntryToIndex(i) +
                      EphemeronHashTable::kEntryKeyIndex;
      int value_index = EphemeronHashTable::EntryToValueIndex(i);
      Object key = table.get(key_index);
      Object value = table.get(value_index);
      SetWeakReference(entry, key_index, key, table.OffsetOfElementAt(key_index));
      SetWeakReference(entry, value_index, value,
                       table.OffsetOfElementAt(value_index));
      HeapEntry* key_entry = GetEntry(key);
      HeapEntry* value_entry = GetEntry(value);
      HeapEntry* table_entry = GetEntry(table);
      if (key_entry && value_entry && !key.IsUndefined()) {
        const char* edge_name = names_->GetFormatted(
            "part of key (%s @%u) -> value (%s @%u) pair in WeakMap (table @%u)",
            key_entry->name(), key_entry->id(), value_entry->name(),
            value_entry->id(), table_entry->id());
        key_entry->SetNamedAutoIndexReference(HeapGraphEdge::kInternal, edge_name,
                                              value_entry, names_);
        table_entry->SetNamedAutoIndexReference(HeapGraphEdge::kInternal,
                                                edge_name, value_entry, names_);
      }
    }
  }
  
  // These static arrays are used to prevent excessive code-size in
  // ExtractContextReferences below, which would happen if we called
  // SetInternalReference for every native context field in a macro.
  static const struct {
    int index;
    const char* name;
  } native_context_names[] = {
  #define CONTEXT_FIELD_INDEX_NAME(index, _, name) {Context::index, #name},
      NATIVE_CONTEXT_FIELDS(CONTEXT_FIELD_INDEX_NAME)
  #undef CONTEXT_FIELD_INDEX_NAME
  };
  
  void V8HeapExplorer::ExtractContextReferences(HeapEntry* entry,
                                                Context context) {
    if (!context.IsNativeContext() && context.is_declaration_context()) {
      ScopeInfo scope_info = context.scope_info();
      // Add context allocated locals.
      int context_locals = scope_info.ContextLocalCount();
      for (int i = 0; i < context_locals; ++i) {
        String local_name = scope_info.ContextLocalName(i);
        int idx = scope_info.ContextHeaderLength() + i;
        SetContextReference(entry, local_name, context.get(idx),
                            Context::OffsetOfElementAt(idx));
      }
      if (scope_info.HasFunctionName()) {
        String name = String::cast(scope_info.FunctionName());
        int idx = scope_info.FunctionContextSlotIndex(name);
        if (idx >= 0) {
          SetContextReference(entry, name, context.get(idx),
                              Context::OffsetOfElementAt(idx));
        }
      }
    }
  
    SetInternalReference(
        entry, "scope_info", context.get(Context::SCOPE_INFO_INDEX),
        FixedArray::OffsetOfElementAt(Context::SCOPE_INFO_INDEX));
    SetInternalReference(entry, "previous", context.get(Context::PREVIOUS_INDEX),
                         FixedArray::OffsetOfElementAt(Context::PREVIOUS_INDEX));
    if (context.has_extension()) {
      SetInternalReference(
          entry, "extension", context.get(Context::EXTENSION_INDEX),
          FixedArray::OffsetOfElementAt(Context::EXTENSION_INDEX));
    }
  
    if (context.IsNativeContext()) {
      TagObject(context.normalized_map_cache(), "(context norm. map cache)");
      TagObject(context.embedder_data(), "(context data)");
      for (size_t i = 0; i < arraysize(native_context_names); i++) {
        int index = native_context_names[i].index;
        const char* name = native_context_names[i].name;
        SetInternalReference(entry, name, context.get(index),
                             FixedArray::OffsetOfElementAt(index));
      }
  
      SetWeakReference(
          entry, "optimized_code_list", context.get(Context::OPTIMIZED_CODE_LIST),
          FixedArray::OffsetOfElementAt(Context::OPTIMIZED_CODE_LIST));
      SetWeakReference(
          entry, "deoptimized_code_list",
          context.get(Context::DEOPTIMIZED_CODE_LIST),
          FixedArray::OffsetOfElementAt(Context::DEOPTIMIZED_CODE_LIST));
      STATIC_ASSERT(Context::OPTIMIZED_CODE_LIST == Context::FIRST_WEAK_SLOT);
      STATIC_ASSERT(Context::NEXT_CONTEXT_LINK + 1 ==
                    Context::NATIVE_CONTEXT_SLOTS);
      STATIC_ASSERT(Context::FIRST_WEAK_SLOT + 3 ==
                    Context::NATIVE_CONTEXT_SLOTS);
    }
  }
  
  void V8HeapExplorer::ExtractMapReferences(HeapEntry* entry, Map map) {
    MaybeObject maybe_raw_transitions_or_prototype_info = map.raw_transitions();
    HeapObject raw_transitions_or_prototype_info;
    if (maybe_raw_transitions_or_prototype_info->GetHeapObjectIfWeak(
            &raw_transitions_or_prototype_info)) {
      DCHECK(raw_transitions_or_prototype_info.IsMap());
      SetWeakReference(entry, "transition", raw_transitions_or_prototype_info,
                       Map::kTransitionsOrPrototypeInfoOffset);
    } else if (maybe_raw_transitions_or_prototype_info->GetHeapObjectIfStrong(
                   &raw_transitions_or_prototype_info)) {
      if (raw_transitions_or_prototype_info.IsTransitionArray()) {
        TransitionArray transitions =
            TransitionArray::cast(raw_transitions_or_prototype_info);
        if (map.CanTransition() && transitions.HasPrototypeTransitions()) {
          TagObject(transitions.GetPrototypeTransitions(),
                    "(prototype transitions)");
        }
        TagObject(transitions, "(transition array)");
        SetInternalReference(entry, "transitions", transitions,
                             Map::kTransitionsOrPrototypeInfoOffset);
      } else if (raw_transitions_or_prototype_info.IsFixedArray()) {
        TagObject(raw_transitions_or_prototype_info, "(transition)");
        SetInternalReference(entry, "transition",
                             raw_transitions_or_prototype_info,
                             Map::kTransitionsOrPrototypeInfoOffset);
      } else if (map.is_prototype_map()) {
        TagObject(raw_transitions_or_prototype_info, "prototype_info");
        SetInternalReference(entry, "prototype_info",
                             raw_transitions_or_prototype_info,
                             Map::kTransitionsOrPrototypeInfoOffset);
      }
    }
    DescriptorArray descriptors = map.instance_descriptors(kRelaxedLoad);
    TagObject(descriptors, "(map descriptors)");
    SetInternalReference(entry, "descriptors", descriptors,
                         Map::kInstanceDescriptorsOffset);
    SetInternalReference(entry, "prototype", map.prototype(),
                         Map::kPrototypeOffset);
    if (FLAG_unbox_double_fields) {
      SetInternalReference(entry, "layout_descriptor",
                           map.layout_descriptor(kAcquireLoad),
                           Map::kLayoutDescriptorOffset);
    }
    if (map.IsContextMap()) {
      Object native_context = map.native_context();
      TagObject(native_context, "(native context)");
      SetInternalReference(entry, "native_context", native_context,
                           Map::kConstructorOrBackPointerOrNativeContextOffset);
    } else {
      Object constructor_or_backpointer = map.constructor_or_backpointer();
      if (constructor_or_backpointer.IsMap()) {
        TagObject(constructor_or_backpointer, "(back pointer)");
        SetInternalReference(entry, "back_pointer", constructor_or_backpointer,
                             Map::kConstructorOrBackPointerOrNativeContextOffset);
      } else if (constructor_or_backpointer.IsFunctionTemplateInfo()) {
        TagObject(constructor_or_backpointer, "(constructor function data)");
        SetInternalReference(entry, "constructor_function_data",
                             constructor_or_backpointer,
                             Map::kConstructorOrBackPointerOrNativeContextOffset);
      } else {
        SetInternalReference(entry, "constructor", constructor_or_backpointer,
                             Map::kConstructorOrBackPointerOrNativeContextOffset);
      }
    }
    TagObject(map.dependent_code(), "(dependent code)");
    SetInternalReference(entry, "dependent_code", map.dependent_code(),
                         Map::kDependentCodeOffset);
  }
  
  void V8HeapExplorer::ExtractSharedFunctionInfoReferences(
      HeapEntry* entry, SharedFunctionInfo shared) {
    String shared_name = shared.DebugName();
    const char* name = nullptr;
    if (shared_name != ReadOnlyRoots(heap_).empty_string()) {
      name = names_->GetName(shared_name);
      TagObject(shared.GetCode(), names_->GetFormatted("(code for %s)", name));
    } else {
      TagObject(shared.GetCode(),
                names_->GetFormatted("(%s code)",
                                     CodeKindToString(shared.GetCode().kind())));
    }
  
    if (shared.name_or_scope_info().IsScopeInfo()) {
      TagObject(shared.name_or_scope_info(), "(function scope info)");
    }
    SetInternalReference(entry, "name_or_scope_info", shared.name_or_scope_info(),
                         SharedFunctionInfo::kNameOrScopeInfoOffset);
    SetInternalReference(entry, "script_or_debug_info",
                         shared.script_or_debug_info(),
                         SharedFunctionInfo::kScriptOrDebugInfoOffset);
    SetInternalReference(entry, "function_data",
                         shared.function_data(kAcquireLoad),
                         SharedFunctionInfo::kFunctionDataOffset);
    SetInternalReference(
        entry, "raw_outer_scope_info_or_feedback_metadata",
        shared.raw_outer_scope_info_or_feedback_metadata(),
        SharedFunctionInfo::kOuterScopeInfoOrFeedbackMetadataOffset);
  }
  
  void V8HeapExplorer::ExtractScriptReferences(HeapEntry* entry, Script script) {
    SetInternalReference(entry, "source", script.source(), Script::kSourceOffset);
    SetInternalReference(entry, "name", script.name(), Script::kNameOffset);
    SetInternalReference(entry, "context_data", script.context_data(),
                         Script::kContextDataOffset);
    TagObject(script.line_ends(), "(script line ends)");
    SetInternalReference(entry, "line_ends", script.line_ends(),
                         Script::kLineEndsOffset);
  }
  
  void V8HeapExplorer::ExtractAccessorInfoReferences(HeapEntry* entry,
                                                     AccessorInfo accessor_info) {
    SetInternalReference(entry, "name", accessor_info.name(),
                         AccessorInfo::kNameOffset);
    SetInternalReference(entry, "expected_receiver_type",
                         accessor_info.expected_receiver_type(),
                         AccessorInfo::kExpectedReceiverTypeOffset);
    SetInternalReference(entry, "getter", accessor_info.getter(),
                         AccessorInfo::kGetterOffset);
    SetInternalReference(entry, "setter", accessor_info.setter(),
                         AccessorInfo::kSetterOffset);
    SetInternalReference(entry, "data", accessor_info.data(),
                         AccessorInfo::kDataOffset);
  }
  
  void V8HeapExplorer::ExtractAccessorPairReferences(HeapEntry* entry,
                                                     AccessorPair accessors) {
    SetInternalReference(entry, "getter", accessors.getter(),
                         AccessorPair::kGetterOffset);
    SetInternalReference(entry, "setter", accessors.setter(),
                         AccessorPair::kSetterOffset);
  }
  
  void V8HeapExplorer::TagBuiltinCodeObject(Code code, const char* name) {
    TagObject(code, names_->GetFormatted("(%s builtin)", name));
  }
  
  void V8HeapExplorer::ExtractCodeReferences(HeapEntry* entry, Code code) {
    TagObject(code.relocation_info(), "(code relocation info)");
    SetInternalReference(entry, "relocation_info", code.relocation_info(),
                         Code::kRelocationInfoOffset);
    TagObject(code.deoptimization_data(), "(code deopt data)");
    SetInternalReference(entry, "deoptimization_data", code.deoptimization_data(),
                         Code::kDeoptimizationDataOffset);
    TagObject(code.source_position_table(), "(source position table)");
    SetInternalReference(entry, "source_position_table",
                         code.source_position_table(),
                         Code::kSourcePositionTableOffset);
  }
  
  void V8HeapExplorer::ExtractCellReferences(HeapEntry* entry, Cell cell) {
    SetInternalReference(entry, "value", cell.value(), Cell::kValueOffset);
  }
  
  void V8HeapExplorer::ExtractFeedbackCellReferences(HeapEntry* entry,
                                                     FeedbackCell feedback_cell) {
    TagObject(feedback_cell, "(feedback cell)");
    SetInternalReference(entry, "value", feedback_cell.value(),
                         FeedbackCell::kValueOffset);
  }
  
  void V8HeapExplorer::ExtractPropertyCellReferences(HeapEntry* entry,
                                                     PropertyCell cell) {
    SetInternalReference(entry, "value", cell.value(),
                         PropertyCell::kValueOffset);
    TagObject(cell.dependent_code(), "(dependent code)");
    SetInternalReference(entry, "dependent_code", cell.dependent_code(),
                         PropertyCell::kDependentCodeOffset);
  }
  
  void V8HeapExplorer::ExtractAllocationSiteReferences(HeapEntry* entry,
                                                       AllocationSite site) {
    SetInternalReference(entry, "transition_info",
                         site.transition_info_or_boilerplate(),
                         AllocationSite::kTransitionInfoOrBoilerplateOffset);
    SetInternalReference(entry, "nested_site", site.nested_site(),
                         AllocationSite::kNestedSiteOffset);
    TagObject(site.dependent_code(), "(dependent code)");
    SetInternalReference(entry, "dependent_code", site.dependent_code(),
                         AllocationSite::kDependentCodeOffset);
  }
  
  void V8HeapExplorer::ExtractArrayBoilerplateDescriptionReferences(
      HeapEntry* entry, ArrayBoilerplateDescription value) {
    SetInternalReference(entry, "constant_elements", value.constant_elements(),
                         ArrayBoilerplateDescription::kConstantElementsOffset);
  }
  
  class JSArrayBufferDataEntryAllocator : public HeapEntriesAllocator {
   public:
    JSArrayBufferDataEntryAllocator(size_t size, V8HeapExplorer* explorer)
        : size_(size)
        , explorer_(explorer) {
    }
    HeapEntry* AllocateEntry(HeapThing ptr) override {
      return explorer_->AddEntry(reinterpret_cast<Address>(ptr),
                                 HeapEntry::kNative, "system / JSArrayBufferData",
                                 size_);
    }
   private:
    size_t size_;
    V8HeapExplorer* explorer_;
  };
  
  void V8HeapExplorer::ExtractJSArrayBufferReferences(HeapEntry* entry,
                                                      JSArrayBuffer buffer) {
    // Setup a reference to a native memory backing_store object.
    if (!buffer.backing_store()) return;
    size_t data_size = buffer.byte_length();
    JSArrayBufferDataEntryAllocator allocator(data_size, this);
    HeapEntry* data_entry =
        generator_->FindOrAddEntry(buffer.backing_store(), &allocator);
    entry->SetNamedReference(HeapGraphEdge::kInternal, "backing_store",
                             data_entry);
  }
  
  void V8HeapExplorer::ExtractJSPromiseReferences(HeapEntry* entry,
                                                  JSPromise promise) {
    SetInternalReference(entry, "reactions_or_result",
                         promise.reactions_or_result(),
                         JSPromise::kReactionsOrResultOffset);
  }
  
  void V8HeapExplorer::ExtractJSGeneratorObjectReferences(
      HeapEntry* entry, JSGeneratorObject generator) {
    SetInternalReference(entry, "function", generator.function(),
                         JSGeneratorObject::kFunctionOffset);
    SetInternalReference(entry, "context", generator.context(),
                         JSGeneratorObject::kContextOffset);
    SetInternalReference(entry, "receiver", generator.receiver(),
                         JSGeneratorObject::kReceiverOffset);
    SetInternalReference(entry, "parameters_and_registers",
                         generator.parameters_and_registers(),
                         JSGeneratorObject::kParametersAndRegistersOffset);
  }
  
  void V8HeapExplorer::ExtractFixedArrayReferences(HeapEntry* entry,
                                                   FixedArray array) {
    for (int i = 0, l = array.length(); i < l; ++i) {
      DCHECK(!HasWeakHeapObjectTag(array.get(i)));
      SetInternalReference(entry, i, array.get(i), array.OffsetOfElementAt(i));
    }
  }
  
  void V8HeapExplorer::ExtractFeedbackVectorReferences(
      HeapEntry* entry, FeedbackVector feedback_vector) {
    MaybeObject code = feedback_vector.optimized_code_weak_or_smi();
    HeapObject code_heap_object;
    if (code->GetHeapObjectIfWeak(&code_heap_object)) {
      SetWeakReference(entry, "optimized code", code_heap_object,
                       FeedbackVector::kOptimizedCodeWeakOrSmiOffset);
    }
  }
  
  void V8HeapExplorer::ExtractDescriptorArrayReferences(HeapEntry* entry,
                                                        DescriptorArray array) {
    SetInternalReference(entry, "enum_cache", array.enum_cache(),
                         DescriptorArray::kEnumCacheOffset);
    MaybeObjectSlot start = MaybeObjectSlot(array.GetDescriptorSlot(0));
    MaybeObjectSlot end = MaybeObjectSlot(
        array.GetDescriptorSlot(array.number_of_all_descriptors()));
    for (int i = 0; start + i < end; ++i) {
      MaybeObjectSlot slot = start + i;
      int offset = static_cast<int>(slot.address() - array.address());
      MaybeObject object = *slot;
      HeapObject heap_object;
      if (object->GetHeapObjectIfWeak(&heap_object)) {
        SetWeakReference(entry, i, heap_object, offset);
      } else if (object->GetHeapObjectIfStrong(&heap_object)) {
        SetInternalReference(entry, i, heap_object, offset);
      }
    }
  }
  
  template <typename T>
  void V8HeapExplorer::ExtractWeakArrayReferences(int header_size,
                                                  HeapEntry* entry, T array) {
    for (int i = 0; i < array.length(); ++i) {
      MaybeObject object = array.Get(i);
      HeapObject heap_object;
      if (object->GetHeapObjectIfWeak(&heap_object)) {
        SetWeakReference(entry, i, heap_object, header_size + i * kTaggedSize);
      } else if (object->GetHeapObjectIfStrong(&heap_object)) {
        SetInternalReference(entry, i, heap_object,
                             header_size + i * kTaggedSize);
      }
    }
  }
  
  void V8HeapExplorer::ExtractPropertyReferences(JSObject js_obj,
                                                 HeapEntry* entry) {
    Isolate* isolate = js_obj.GetIsolate();
    if (js_obj.HasFastProperties()) {
      DescriptorArray descs = js_obj.map().instance_descriptors(kRelaxedLoad);
      for (InternalIndex i : js_obj.map().IterateOwnDescriptors()) {
        PropertyDetails details = descs.GetDetails(i);
        switch (details.location()) {
          case kField: {
            Representation r = details.representation();
            if (r.IsSmi() || r.IsDouble()) break;
  
            Name k = descs.GetKey(i);
            FieldIndex field_index = FieldIndex::ForDescriptor(js_obj.map(), i);
            Object value = js_obj.RawFastPropertyAt(field_index);
            int field_offset =
                field_index.is_inobject() ? field_index.offset() : -1;
  
            SetDataOrAccessorPropertyReference(details.kind(), entry, k, value,
                                               nullptr, field_offset);
            break;
          }
          case kDescriptor:
            SetDataOrAccessorPropertyReference(
                details.kind(), entry, descs.GetKey(i), descs.GetStrongValue(i));
            break;
        }
      }
    } else if (js_obj.IsJSGlobalObject()) {
      // We assume that global objects can only have slow properties.
      GlobalDictionary dictionary =
          JSGlobalObject::cast(js_obj).global_dictionary();
      ReadOnlyRoots roots(isolate);
      for (InternalIndex i : dictionary.IterateEntries()) {
        if (!dictionary.IsKey(roots, dictionary.KeyAt(i))) continue;
        PropertyCell cell = dictionary.CellAt(i);
        Name name = cell.name();
        Object value = cell.value();
        PropertyDetails details = cell.property_details();
        SetDataOrAccessorPropertyReference(details.kind(), entry, name, value);
      }
    } else {
      NameDictionary dictionary = js_obj.property_dictionary();
      ReadOnlyRoots roots(isolate);
      for (InternalIndex i : dictionary.IterateEntries()) {
        Object k = dictionary.KeyAt(i);
        if (!dictionary.IsKey(roots, k)) continue;
        Object value = dictionary.ValueAt(i);
        PropertyDetails details = dictionary.DetailsAt(i);
        SetDataOrAccessorPropertyReference(details.kind(), entry, Name::cast(k),
                                           value);
      }
    }
  }
  
  void V8HeapExplorer::ExtractAccessorPairProperty(HeapEntry* entry, Name key,
                                                   Object callback_obj,
                                                   int field_offset) {
    if (!callback_obj.IsAccessorPair()) return;
    AccessorPair accessors = AccessorPair::cast(callback_obj);
    SetPropertyReference(entry, key, accessors, nullptr, field_offset);
    Object getter = accessors.getter();
    if (!getter.IsOddball()) {
      SetPropertyReference(entry, key, getter, "get %s");
    }
    Object setter = accessors.setter();
    if (!setter.IsOddball()) {
      SetPropertyReference(entry, key, setter, "set %s");
    }
  }
  
  void V8HeapExplorer::ExtractElementReferences(JSObject js_obj,
                                                HeapEntry* entry) {
    ReadOnlyRoots roots = js_obj.GetReadOnlyRoots();
    if (js_obj.HasObjectElements()) {
      FixedArray elements = FixedArray::cast(js_obj.elements());
      int length = js_obj.IsJSArray() ? Smi::ToInt(JSArray::cast(js_obj).length())
                                      : elements.length();
      for (int i = 0; i < length; ++i) {
        if (!elements.get(i).IsTheHole(roots)) {
          SetElementReference(entry, i, elements.get(i));
        }
      }
    } else if (js_obj.HasDictionaryElements()) {
      NumberDictionary dictionary = js_obj.element_dictionary();
      for (InternalIndex i : dictionary.IterateEntries()) {
        Object k = dictionary.KeyAt(i);
        if (!dictionary.IsKey(roots, k)) continue;
        DCHECK(k.IsNumber());
        uint32_t index = static_cast<uint32_t>(k.Number());
        SetElementReference(entry, index, dictionary.ValueAt(i));
      }
    }
  }
  
  void V8HeapExplorer::ExtractInternalReferences(JSObject js_obj,
                                                 HeapEntry* entry) {
    int length = js_obj.GetEmbedderFieldCount();
    for (int i = 0; i < length; ++i) {
      Object o = js_obj.GetEmbedderField(i);
      SetInternalReference(entry, i, o, js_obj.GetEmbedderFieldOffset(i));
    }
  }
  
  JSFunction V8HeapExplorer::GetConstructor(JSReceiver receiver) {
    Isolate* isolate = receiver.GetIsolate();
    DisallowHeapAllocation no_gc;
    HandleScope scope(isolate);
    MaybeHandle<JSFunction> maybe_constructor =
        JSReceiver::GetConstructor(handle(receiver, isolate));
  
    if (maybe_constructor.is_null()) return JSFunction();
  
    return *maybe_constructor.ToHandleChecked();
  }
  
  String V8HeapExplorer::GetConstructorName(JSObject object) {
    Isolate* isolate = object.GetIsolate();
    if (object.IsJSFunction()) return ReadOnlyRoots(isolate).closure_string();
    DisallowHeapAllocation no_gc;
    HandleScope scope(isolate);
    return *JSReceiver::GetConstructorName(handle(object, isolate));
  }
  
  HeapEntry* V8HeapExplorer::GetEntry(Object obj) {
    return obj.IsHeapObject() ? generator_->FindOrAddEntry(
                                    reinterpret_cast<void*>(obj.ptr()), this)
                              : nullptr;
  }
  
  class RootsReferencesExtractor : public RootVisitor {
   public:
    explicit RootsReferencesExtractor(V8HeapExplorer* explorer)
        : explorer_(explorer), visiting_weak_roots_(false) {}
  
    void SetVisitingWeakRoots() { visiting_weak_roots_ = true; }
  
    void VisitRootPointer(Root root, const char* description,
                          FullObjectSlot object) override {
      if (root == Root::kBuiltins) {
        explorer_->TagBuiltinCodeObject(Code::cast(*object), description);
      }
      explorer_->SetGcSubrootReference(root, description, visiting_weak_roots_,
                                       *object);
    }
  
    void VisitRootPointers(Root root, const char* description,
                           FullObjectSlot start, FullObjectSlot end) override {
      for (FullObjectSlot p = start; p < end; ++p) {
        VisitRootPointer(root, description, p);
      }
    }
  
    void VisitRootPointers(Root root, const char* description,
                           OffHeapObjectSlot start,
                           OffHeapObjectSlot end) override {
      DCHECK_EQ(root, Root::kStringTable);
      IsolateRoot isolate = Isolate::FromHeap(explorer_->heap_);
      for (OffHeapObjectSlot p = start; p < end; ++p) {
        explorer_->SetGcSubrootReference(root, description, visiting_weak_roots_,
                                         p.load(isolate));
      }
    }
  
   private:
    V8HeapExplorer* explorer_;
    bool visiting_weak_roots_;
  };
  
  bool V8HeapExplorer::IterateAndExtractReferences(
      HeapSnapshotGenerator* generator) {
    generator_ = generator;
  
    // Create references to the synthetic roots.
    SetRootGcRootsReference();
    for (int root = 0; root < static_cast<int>(Root::kNumberOfRoots); root++) {
      SetGcRootsReference(static_cast<Root>(root));
    }
  
    // Make sure builtin code objects get their builtin tags
    // first. Otherwise a particular JSFunction object could set
    // its custom name to a generic builtin.
    RootsReferencesExtractor extractor(this);
    ReadOnlyRoots(heap_).Iterate(&extractor);
    heap_->IterateRoots(&extractor, base::EnumSet<SkipRoot>{SkipRoot::kWeak});
    // TODO(ulan): The heap snapshot generator incorrectly considers the weak
    // string tables as strong retainers. Move IterateWeakRoots after
    // SetVisitingWeakRoots.
    heap_->IterateWeakRoots(&extractor, {});
    extractor.SetVisitingWeakRoots();
    heap_->IterateWeakGlobalHandles(&extractor);
  
    bool interrupted = false;
  
    CombinedHeapObjectIterator iterator(heap_,
                                        HeapObjectIterator::kFilterUnreachable);
    // Heap iteration with filtering must be finished in any case.
    for (HeapObject obj = iterator.Next(); !obj.is_null();
         obj = iterator.Next(), progress_->ProgressStep()) {
      if (interrupted) continue;
  
      size_t max_pointer = obj.Size() / kTaggedSize;
      if (max_pointer > visited_fields_.size()) {
        // Clear the current bits.
        std::vector<bool>().swap(visited_fields_);
        // Reallocate to right size.
        visited_fields_.resize(max_pointer, false);
      }
  
      HeapEntry* entry = GetEntry(obj);
      ExtractReferences(entry, obj);
      SetInternalReference(entry, "map", obj.map(), HeapObject::kMapOffset);
      // Extract unvisited fields as hidden references and restore tags
      // of visited fields.
      IndexedReferencesExtractor refs_extractor(this, obj, entry);
      obj.Iterate(&refs_extractor);
  
      // Ensure visited_fields_ doesn't leak to the next object.
      for (size_t i = 0; i < max_pointer; ++i) {
        DCHECK(!visited_fields_[i]);
      }
  
      // Extract location for specific object types
      ExtractLocation(entry, obj);
  
      if (!progress_->ProgressReport(false)) interrupted = true;
    }
  
    generator_ = nullptr;
    return interrupted ? false : progress_->ProgressReport(true);
  }
  
  bool V8HeapExplorer::IsEssentialObject(Object object) {
    ReadOnlyRoots roots(heap_);
    return object.IsHeapObject() && !object.IsOddball() &&
           object != roots.empty_byte_array() &&
           object != roots.empty_fixed_array() &&
           object != roots.empty_weak_fixed_array() &&
           object != roots.empty_descriptor_array() &&
           object != roots.fixed_array_map() && object != roots.cell_map() &&
           object != roots.global_property_cell_map() &&
           object != roots.shared_function_info_map() &&
           object != roots.free_space_map() &&
           object != roots.one_pointer_filler_map() &&
           object != roots.two_pointer_filler_map();
  }
  
  bool V8HeapExplorer::IsEssentialHiddenReference(Object parent,
                                                  int field_offset) {
    if (parent.IsAllocationSite() &&
        field_offset == AllocationSite::kWeakNextOffset)
      return false;
    if (parent.IsCodeDataContainer() &&
        field_offset == CodeDataContainer::kNextCodeLinkOffset)
      return false;
    if (parent.IsContext() &&
        field_offset == Context::OffsetOfElementAt(Context::NEXT_CONTEXT_LINK))
      return false;
    return true;
  }
  
  void V8HeapExplorer::SetContextReference(HeapEntry* parent_entry,
                                           String reference_name,
                                           Object child_obj, int field_offset) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    parent_entry->SetNamedReference(HeapGraphEdge::kContextVariable,
                                    names_->GetName(reference_name), child_entry);
    MarkVisitedField(field_offset);
  }
  
  void V8HeapExplorer::MarkVisitedField(int offset) {
    if (offset < 0) return;
    int index = offset / kTaggedSize;
    DCHECK(!visited_fields_[index]);
    visited_fields_[index] = true;
  }
  
  void V8HeapExplorer::SetNativeBindReference(HeapEntry* parent_entry,
                                              const char* reference_name,
                                              Object child_obj) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    parent_entry->SetNamedReference(HeapGraphEdge::kShortcut, reference_name,
                                    child_entry);
  }
  
  void V8HeapExplorer::SetElementReference(HeapEntry* parent_entry, int index,
                                           Object child_obj) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    parent_entry->SetIndexedReference(HeapGraphEdge::kElement, index,
                                      child_entry);
  }
  
  void V8HeapExplorer::SetInternalReference(HeapEntry* parent_entry,
                                            const char* reference_name,
                                            Object child_obj, int field_offset) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    if (IsEssentialObject(child_obj)) {
      parent_entry->SetNamedReference(HeapGraphEdge::kInternal, reference_name,
                                      child_entry);
    }
    MarkVisitedField(field_offset);
  }
  
  void V8HeapExplorer::SetInternalReference(HeapEntry* parent_entry, int index,
                                            Object child_obj, int field_offset) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    if (IsEssentialObject(child_obj)) {
      parent_entry->SetNamedReference(HeapGraphEdge::kInternal,
                                      names_->GetName(index), child_entry);
    }
    MarkVisitedField(field_offset);
  }
  
  void V8HeapExplorer::SetHiddenReference(HeapObject parent_obj,
                                          HeapEntry* parent_entry, int index,
                                          Object child_obj, int field_offset) {
    DCHECK_EQ(parent_entry, GetEntry(parent_obj));
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry != nullptr && IsEssentialObject(child_obj) &&
        IsEssentialHiddenReference(parent_obj, field_offset)) {
      parent_entry->SetIndexedReference(HeapGraphEdge::kHidden, index,
                                        child_entry);
    }
  }
  
  void V8HeapExplorer::SetWeakReference(HeapEntry* parent_entry,
                                        const char* reference_name,
                                        Object child_obj, int field_offset) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    if (IsEssentialObject(child_obj)) {
      parent_entry->SetNamedReference(HeapGraphEdge::kWeak, reference_name,
                                      child_entry);
    }
    MarkVisitedField(field_offset);
  }
  
  void V8HeapExplorer::SetWeakReference(HeapEntry* parent_entry, int index,
                                        Object child_obj, int field_offset) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    if (IsEssentialObject(child_obj)) {
      parent_entry->SetNamedReference(
          HeapGraphEdge::kWeak, names_->GetFormatted("%d", index), child_entry);
    }
    MarkVisitedField(field_offset);
  }
  
  void V8HeapExplorer::SetDataOrAccessorPropertyReference(
      PropertyKind kind, HeapEntry* parent_entry, Name reference_name,
      Object child_obj, const char* name_format_string, int field_offset) {
    if (kind == kAccessor) {
      ExtractAccessorPairProperty(parent_entry, reference_name, child_obj,
                                  field_offset);
    } else {
      SetPropertyReference(parent_entry, reference_name, child_obj,
                           name_format_string, field_offset);
    }
  }
  
  void V8HeapExplorer::SetPropertyReference(HeapEntry* parent_entry,
                                            Name reference_name, Object child_obj,
                                            const char* name_format_string,
                                            int field_offset) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    HeapGraphEdge::Type type =
        reference_name.IsSymbol() || String::cast(reference_name).length() > 0
            ? HeapGraphEdge::kProperty
            : HeapGraphEdge::kInternal;
    const char* name =
        name_format_string != nullptr && reference_name.IsString()
            ? names_->GetFormatted(
                  name_format_string,
                  String::cast(reference_name)
                      .ToCString(DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL)
                      .get())
            : names_->GetName(reference_name);
  
    parent_entry->SetNamedReference(type, name, child_entry);
    MarkVisitedField(field_offset);
  }
  
  void V8HeapExplorer::SetRootGcRootsReference() {
    snapshot_->root()->SetIndexedAutoIndexReference(HeapGraphEdge::kElement,
                                                    snapshot_->gc_roots());
  }
  
  void V8HeapExplorer::SetUserGlobalReference(Object child_obj) {
    HeapEntry* child_entry = GetEntry(child_obj);
    DCHECK_NOT_NULL(child_entry);
    snapshot_->root()->SetNamedAutoIndexReference(HeapGraphEdge::kShortcut,
                                                  nullptr, child_entry, names_);
  }
  
  void V8HeapExplorer::SetGcRootsReference(Root root) {
    snapshot_->gc_roots()->SetIndexedAutoIndexReference(
        HeapGraphEdge::kElement, snapshot_->gc_subroot(root));
  }
  
  void V8HeapExplorer::SetGcSubrootReference(Root root, const char* description,
                                             bool is_weak, Object child_obj) {
    HeapEntry* child_entry = GetEntry(child_obj);
    if (child_entry == nullptr) return;
    const char* name = GetStrongGcSubrootName(child_obj);
    HeapGraphEdge::Type edge_type =
        is_weak ? HeapGraphEdge::kWeak : HeapGraphEdge::kInternal;
    if (name != nullptr) {
      snapshot_->gc_subroot(root)->SetNamedReference(edge_type, name,
                                                     child_entry);
    } else {
      snapshot_->gc_subroot(root)->SetNamedAutoIndexReference(
          edge_type, description, child_entry, names_);
    }
  
    // For full heap snapshots we do not emit user roots but rather rely on
    // regular GC roots to retain objects.
    if (!snapshot_->treat_global_objects_as_roots()) return;
  
    // Add a shortcut to JS global object reference at snapshot root.
    // That allows the user to easily find global objects. They are
    // also used as starting points in distance calculations.
    if (is_weak || !child_obj.IsNativeContext()) return;
  
    JSGlobalObject global = Context::cast(child_obj).global_object();
    if (!global.IsJSGlobalObject()) return;
  
    if (!user_roots_.insert(global).second) return;
  
    SetUserGlobalReference(global);
  }
  
  const char* V8HeapExplorer::GetStrongGcSubrootName(Object object) {
    if (strong_gc_subroot_names_.empty()) {
      Isolate* isolate = Isolate::FromHeap(heap_);
      for (RootIndex root_index = RootIndex::kFirstStrongOrReadOnlyRoot;
           root_index <= RootIndex::kLastStrongOrReadOnlyRoot; ++root_index) {
        const char* name = RootsTable::name(root_index);
        strong_gc_subroot_names_.emplace(isolate->root(root_index), name);
      }
      CHECK(!strong_gc_subroot_names_.empty());
    }
    auto it = strong_gc_subroot_names_.find(object);
    return it != strong_gc_subroot_names_.end() ? it->second : nullptr;
  }
  
  void V8HeapExplorer::TagObject(Object obj, const char* tag) {
    if (IsEssentialObject(obj)) {
      HeapEntry* entry = GetEntry(obj);
      if (entry->name()[0] == '\0') {
        entry->set_name(tag);
      }
    }
  }
  
  class GlobalObjectsEnumerator : public RootVisitor {
   public:
    explicit GlobalObjectsEnumerator(Isolate* isolate) : isolate_(isolate) {}
  
    void VisitRootPointers(Root root, const char* description,
                           FullObjectSlot start, FullObjectSlot end) override {
      VisitRootPointersImpl(root, description, start, end);
    }
  
    void VisitRootPointers(Root root, const char* description,
                           OffHeapObjectSlot start,
                           OffHeapObjectSlot end) override {
      VisitRootPointersImpl(root, description, start, end);
    }
  
    int count() const { return static_cast<int>(objects_.size()); }
    Handle<JSGlobalObject>& at(int i) { return objects_[i]; }
  
   private:
    template <typename TSlot>
    void VisitRootPointersImpl(Root root, const char* description, TSlot start,
                               TSlot end) {
      for (TSlot p = start; p < end; ++p) {
        Object o = p.load(isolate_);
        if (!o.IsNativeContext(isolate_)) continue;
        JSObject proxy = Context::cast(o).global_proxy();
        if (!proxy.IsJSGlobalProxy(isolate_)) continue;
        Object global = proxy.map(isolate_).prototype(isolate_);
        if (!global.IsJSGlobalObject(isolate_)) continue;
        objects_.push_back(handle(JSGlobalObject::cast(global), isolate_));
      }
    }
  
    Isolate* isolate_;
    std::vector<Handle<JSGlobalObject>> objects_;
  };
  
  
  // Modifies heap. Must not be run during heap traversal.
  void V8HeapExplorer::TagGlobalObjects() {
    Isolate* isolate = Isolate::FromHeap(heap_);
    HandleScope scope(isolate);
    GlobalObjectsEnumerator enumerator(isolate);
    isolate->global_handles()->IterateAllRoots(&enumerator);
    std::vector<const char*> urls(enumerator.count());
    for (int i = 0, l = enumerator.count(); i < l; ++i) {
      urls[i] = global_object_name_resolver_
                    ? global_object_name_resolver_->GetName(Utils::ToLocal(
                          Handle<JSObject>::cast(enumerator.at(i))))
                    : nullptr;
    }
  
    DisallowHeapAllocation no_allocation;
    for (int i = 0, l = enumerator.count(); i < l; ++i) {
      if (urls[i]) objects_tags_.emplace(*enumerator.at(i), urls[i]);
    }
  }
  
  class EmbedderGraphImpl : public EmbedderGraph {
   public:
    struct Edge {
      Node* from;
      Node* to;
      const char* name;
    };
  
    class V8NodeImpl : public Node {
     public:
      explicit V8NodeImpl(Object object) : object_(object) {}
      Object GetObject() { return object_; }
  
      // Node overrides.
      bool IsEmbedderNode() override { return false; }
      const char* Name() override {
        // The name should be retrieved via GetObject().
        UNREACHABLE();
        return "";
      }
      size_t SizeInBytes() override {
        // The size should be retrieved via GetObject().
        UNREACHABLE();
        return 0;
      }
  
     private:
      Object object_;
    };
  
    Node* V8Node(const v8::Local<v8::Value>& value) final {
      Handle<Object> object = v8::Utils::OpenHandle(*value);
      DCHECK(!object.is_null());
      return AddNode(std::unique_ptr<Node>(new V8NodeImpl(*object)));
    }
  
    Node* AddNode(std::unique_ptr<Node> node) final {
      Node* result = node.get();
      nodes_.push_back(std::move(node));
      return result;
    }
  
    void AddEdge(Node* from, Node* to, const char* name) final {
      edges_.push_back({from, to, name});
    }
  
    const std::vector<std::unique_ptr<Node>>& nodes() { return nodes_; }
    const std::vector<Edge>& edges() { return edges_; }
  
   private:
    std::vector<std::unique_ptr<Node>> nodes_;
    std::vector<Edge> edges_;
  };
  
  class EmbedderGraphEntriesAllocator : public HeapEntriesAllocator {
   public:
    explicit EmbedderGraphEntriesAllocator(HeapSnapshot* snapshot)
        : snapshot_(snapshot),
          names_(snapshot_->profiler()->names()),
          heap_object_map_(snapshot_->profiler()->heap_object_map()) {}
    HeapEntry* AllocateEntry(HeapThing ptr) override;
  
   private:
    HeapSnapshot* snapshot_;
    StringsStorage* names_;
    HeapObjectsMap* heap_object_map_;
  };
  
  namespace {
  
  const char* EmbedderGraphNodeName(StringsStorage* names,
                                    EmbedderGraphImpl::Node* node) {
    const char* prefix = node->NamePrefix();
    return prefix ? names->GetFormatted("%s %s", prefix, node->Name())
                  : names->GetCopy(node->Name());
  }
  
  HeapEntry::Type EmbedderGraphNodeType(EmbedderGraphImpl::Node* node) {
    return node->IsRootNode() ? HeapEntry::kSynthetic : HeapEntry::kNative;
  }
  
  // Merges the names of an embedder node and its wrapper node.
  // If the wrapper node name contains a tag suffix (part after '/') then the
  // result is the embedder node name concatenated with the tag suffix.
  // Otherwise, the result is the embedder node name.
  const char* MergeNames(StringsStorage* names, const char* embedder_name,
                         const char* wrapper_name) {
    const char* suffix = strchr(wrapper_name, '/');
    return suffix ? names->GetFormatted("%s %s", embedder_name, suffix)
                  : embedder_name;
  }
  
  }  // anonymous namespace
  
  HeapEntry* EmbedderGraphEntriesAllocator::AllocateEntry(HeapThing ptr) {
    EmbedderGraphImpl::Node* node =
        reinterpret_cast<EmbedderGraphImpl::Node*>(ptr);
    DCHECK(node->IsEmbedderNode());
    size_t size = node->SizeInBytes();
    Address lookup_address = reinterpret_cast<Address>(node->GetNativeObject());
    SnapshotObjectId id =
        (lookup_address) ? heap_object_map_->FindOrAddEntry(lookup_address, 0)
                         : static_cast<SnapshotObjectId>(
                               reinterpret_cast<uintptr_t>(node) << 1);
    auto* heap_entry = snapshot_->AddEntry(EmbedderGraphNodeType(node),
                                           EmbedderGraphNodeName(names_, node),
                                           id, static_cast<int>(size), 0);
    heap_entry->set_detachedness(node->GetDetachedness());
    return heap_entry;
  }
  
  NativeObjectsExplorer::NativeObjectsExplorer(
      HeapSnapshot* snapshot, SnapshottingProgressReportingInterface* progress)
      : isolate_(
            Isolate::FromHeap(snapshot->profiler()->heap_object_map()->heap())),
        snapshot_(snapshot),
        names_(snapshot_->profiler()->names()),
        heap_object_map_(snapshot_->profiler()->heap_object_map()),
        embedder_graph_entries_allocator_(
            new EmbedderGraphEntriesAllocator(snapshot)) {}
  
  void NativeObjectsExplorer::MergeNodeIntoEntry(
      HeapEntry* entry, EmbedderGraph::Node* original_node,
      EmbedderGraph::Node* wrapper_node) {
    // The wrapper node may be an embedder node (for testing purposes) or a V8
    // node (production code).
    if (!wrapper_node->IsEmbedderNode()) {
      // For V8 nodes only we can add a lookup.
      EmbedderGraphImpl::V8NodeImpl* v8_node =
          static_cast<EmbedderGraphImpl::V8NodeImpl*>(wrapper_node);
      Object object = v8_node->GetObject();
      DCHECK(!object.IsSmi());
      if (original_node->GetNativeObject()) {
        HeapObject heap_object = HeapObject::cast(object);
        heap_object_map_->AddMergedNativeEntry(original_node->GetNativeObject(),
                                               heap_object.address());
        DCHECK_EQ(entry->id(), heap_object_map_->FindMergedNativeEntry(
                                   original_node->GetNativeObject()));
      }
    }
    entry->set_detachedness(original_node->GetDetachedness());
    entry->set_name(MergeNames(
        names_, EmbedderGraphNodeName(names_, original_node), entry->name()));
    entry->set_type(EmbedderGraphNodeType(original_node));
  }
  
  HeapEntry* NativeObjectsExplorer::EntryForEmbedderGraphNode(
      EmbedderGraphImpl::Node* node) {
    // Return the entry for the wrapper node if present.
    if (node->WrapperNode()) {
      node = node->WrapperNode();
    }
    // Node is EmbedderNode.
    if (node->IsEmbedderNode()) {
      return generator_->FindOrAddEntry(node,
                                        embedder_graph_entries_allocator_.get());
    }
    // Node is V8NodeImpl.
    Object object =
        static_cast<EmbedderGraphImpl::V8NodeImpl*>(node)->GetObject();
    if (object.IsSmi()) return nullptr;
    auto* entry = generator_->FindEntry(
        reinterpret_cast<void*>(Object::cast(object).ptr()));
    return entry;
  }
  
  bool NativeObjectsExplorer::IterateAndExtractReferences(
      HeapSnapshotGenerator* generator) {
    generator_ = generator;
  
    if (FLAG_heap_profiler_use_embedder_graph &&
        snapshot_->profiler()->HasBuildEmbedderGraphCallback()) {
      v8::HandleScope scope(reinterpret_cast<v8::Isolate*>(isolate_));
      DisallowHeapAllocation no_allocation;
      EmbedderGraphImpl graph;
      snapshot_->profiler()->BuildEmbedderGraph(isolate_, &graph);
      for (const auto& node : graph.nodes()) {
        // Only add embedder nodes as V8 nodes have been added already by the
        // V8HeapExplorer.
        if (!node->IsEmbedderNode()) continue;
  
        if (auto* entry = EntryForEmbedderGraphNode(node.get())) {
          if (node->IsRootNode()) {
            snapshot_->root()->SetIndexedAutoIndexReference(
                HeapGraphEdge::kElement, entry);
          }
          if (node->WrapperNode()) {
            MergeNodeIntoEntry(entry, node.get(), node->WrapperNode());
          }
        }
      }
      // Fill edges of the graph.
      for (const auto& edge : graph.edges()) {
        // |from| and |to| can be nullptr if the corresponding node is a V8 node
        // pointing to a Smi.
        HeapEntry* from = EntryForEmbedderGraphNode(edge.from);
        if (!from) continue;
        HeapEntry* to = EntryForEmbedderGraphNode(edge.to);
        if (!to) continue;
        if (edge.name == nullptr) {
          from->SetIndexedAutoIndexReference(HeapGraphEdge::kElement, to);
        } else {
          from->SetNamedReference(HeapGraphEdge::kInternal,
                                  names_->GetCopy(edge.name), to);
        }
      }
    }
    generator_ = nullptr;
    return true;
  }
  
  HeapSnapshotGenerator::HeapSnapshotGenerator(
      HeapSnapshot* snapshot,
      v8::ActivityControl* control,
      v8::HeapProfiler::ObjectNameResolver* resolver,
      Heap* heap)
      : snapshot_(snapshot),
        control_(control),
        v8_heap_explorer_(snapshot_, this, resolver),
        dom_explorer_(snapshot_, this),
        heap_(heap) {
  }
  
  namespace {
  class NullContextForSnapshotScope {
   public:
    explicit NullContextForSnapshotScope(Isolate* isolate)
        : isolate_(isolate), prev_(isolate->context()) {
      isolate_->set_context(Context());
    }
    ~NullContextForSnapshotScope() { isolate_->set_context(prev_); }
  
   private:
    Isolate* isolate_;
    Context prev_;
  };
  }  // namespace
  
  bool HeapSnapshotGenerator::GenerateSnapshot() {
    v8_heap_explorer_.TagGlobalObjects();
  
    // TODO(1562) Profiler assumes that any object that is in the heap after
    // full GC is reachable from the root when computing dominators.
    // This is not true for weakly reachable objects.
    // As a temporary solution we call GC twice.
    heap_->PreciseCollectAllGarbage(Heap::kNoGCFlags,
                                    GarbageCollectionReason::kHeapProfiler);
    heap_->PreciseCollectAllGarbage(Heap::kNoGCFlags,
                                    GarbageCollectionReason::kHeapProfiler);
  
    NullContextForSnapshotScope null_context_scope(Isolate::FromHeap(heap_));
    SafepointScope scope(heap_);
  
  #ifdef VERIFY_HEAP
    Heap* debug_heap = heap_;
    if (FLAG_verify_heap) {
      debug_heap->Verify();
    }
  #endif
  
    InitProgressCounter();
  
  #ifdef VERIFY_HEAP
    if (FLAG_verify_heap) {
      debug_heap->Verify();
    }
  #endif
  
    snapshot_->AddSyntheticRootEntries();
  
    if (!FillReferences()) return false;
  
    snapshot_->FillChildren();
    snapshot_->RememberLastJSObjectId();
  
    progress_counter_ = progress_total_;
    if (!ProgressReport(true)) return false;
    return true;
  }
  
  void HeapSnapshotGenerator::ProgressStep() {
    ++progress_counter_;
  }
  
  bool HeapSnapshotGenerator::ProgressReport(bool force) {
    const int kProgressReportGranularity = 10000;
    if (control_ != nullptr &&
        (force || progress_counter_ % kProgressReportGranularity == 0)) {
      return control_->ReportProgressValue(progress_counter_, progress_total_) ==
             v8::ActivityControl::kContinue;
    }
    return true;
  }
  
  void HeapSnapshotGenerator::InitProgressCounter() {
    if (control_ == nullptr) return;
    // The +1 ensures that intermediate ProgressReport calls will never signal
    // that the work is finished (i.e. progress_counter_ == progress_total_).
    // Only the forced ProgressReport() at the end of GenerateSnapshot()
    // should signal that the work is finished because signalling finished twice
    // breaks the DevTools frontend.
    progress_total_ = v8_heap_explorer_.EstimateObjectsCount() + 1;
    progress_counter_ = 0;
  }
  
  bool HeapSnapshotGenerator::FillReferences() {
    return v8_heap_explorer_.IterateAndExtractReferences(this) &&
           dom_explorer_.IterateAndExtractReferences(this);
  }
  
  template<int bytes> struct MaxDecimalDigitsIn;
  template <>
  struct MaxDecimalDigitsIn<1> {
    static const int kSigned = 3;
    static const int kUnsigned = 3;
  };
  template<> struct MaxDecimalDigitsIn<4> {
    static const int kSigned = 11;
    static const int kUnsigned = 10;
  };
  template<> struct MaxDecimalDigitsIn<8> {
    static const int kSigned = 20;
    static const int kUnsigned = 20;
  };
  
  class OutputStreamWriter {
   public:
    explicit OutputStreamWriter(v8::OutputStream* stream)
        : stream_(stream),
          chunk_size_(stream->GetChunkSize()),
          chunk_(chunk_size_),
          chunk_pos_(0),
          aborted_(false) {
      DCHECK_GT(chunk_size_, 0);
    }
    bool aborted() { return aborted_; }
    void AddCharacter(char c) {
      DCHECK_NE(c, '\0');
      DCHECK(chunk_pos_ < chunk_size_);
      chunk_[chunk_pos_++] = c;
      MaybeWriteChunk();
    }
    void AddString(const char* s) {
      size_t len = strlen(s);
      DCHECK_GE(kMaxInt, len);
      AddSubstring(s, static_cast<int>(len));
    }
    void AddSubstring(const char* s, int n) {
      if (n <= 0) return;
      DCHECK_LE(n, strlen(s));
      const char* s_end = s + n;
      while (s < s_end) {
        int s_chunk_size =
            Min(chunk_size_ - chunk_pos_, static_cast<int>(s_end - s));
        DCHECK_GT(s_chunk_size, 0);
        MemCopy(chunk_.begin() + chunk_pos_, s, s_chunk_size);
        s += s_chunk_size;
        chunk_pos_ += s_chunk_size;
        MaybeWriteChunk();
      }
    }
    void AddNumber(unsigned n) { AddNumberImpl<unsigned>(n, "%u"); }
    void Finalize() {
      if (aborted_) return;
      DCHECK(chunk_pos_ < chunk_size_);
      if (chunk_pos_ != 0) {
        WriteChunk();
      }
      stream_->EndOfStream();
    }
  
   private:
    template<typename T>
    void AddNumberImpl(T n, const char* format) {
      // Buffer for the longest value plus trailing \0
      static const int kMaxNumberSize =
          MaxDecimalDigitsIn<sizeof(T)>::kUnsigned + 1;
      if (chunk_size_ - chunk_pos_ >= kMaxNumberSize) {
        int result = SNPrintF(
            chunk_.SubVector(chunk_pos_, chunk_size_), format, n);
        DCHECK_NE(result, -1);
        chunk_pos_ += result;
        MaybeWriteChunk();
      } else {
        EmbeddedVector<char, kMaxNumberSize> buffer;
        int result = SNPrintF(buffer, format, n);
        USE(result);
        DCHECK_NE(result, -1);
        AddString(buffer.begin());
      }
    }
    void MaybeWriteChunk() {
      DCHECK(chunk_pos_ <= chunk_size_);
      if (chunk_pos_ == chunk_size_) {
        WriteChunk();
      }
    }
    void WriteChunk() {
      if (aborted_) return;
      if (stream_->WriteAsciiChunk(chunk_.begin(), chunk_pos_) ==
          v8::OutputStream::kAbort)
        aborted_ = true;
      chunk_pos_ = 0;
    }
  
    v8::OutputStream* stream_;
    int chunk_size_;
    ScopedVector<char> chunk_;
    int chunk_pos_;
    bool aborted_;
  };
  
  
  // type, name|index, to_node.
  const int HeapSnapshotJSONSerializer::kEdgeFieldsCount = 3;
  // type, name, id, self_size, edge_count, trace_node_id, detachedness.
  const int HeapSnapshotJSONSerializer::kNodeFieldsCount = 7;
  
  void HeapSnapshotJSONSerializer::Serialize(v8::OutputStream* stream) {
    if (AllocationTracker* allocation_tracker =
        snapshot_->profiler()->allocation_tracker()) {
      allocation_tracker->PrepareForSerialization();
    }
    DCHECK_NULL(writer_);
    writer_ = new OutputStreamWriter(stream);
    SerializeImpl();
    delete writer_;
    writer_ = nullptr;
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeImpl() {
    DCHECK_EQ(0, snapshot_->root()->index());
    writer_->AddCharacter('{');
    writer_->AddString("\"snapshot\":{");
    SerializeSnapshot();
    if (writer_->aborted()) return;
    writer_->AddString("},\n");
    writer_->AddString("\"nodes\":[");
    SerializeNodes();
    if (writer_->aborted()) return;
    writer_->AddString("],\n");
    writer_->AddString("\"edges\":[");
    SerializeEdges();
    if (writer_->aborted()) return;
    writer_->AddString("],\n");
  
    writer_->AddString("\"trace_function_infos\":[");
    SerializeTraceNodeInfos();
    if (writer_->aborted()) return;
    writer_->AddString("],\n");
    writer_->AddString("\"trace_tree\":[");
    SerializeTraceTree();
    if (writer_->aborted()) return;
    writer_->AddString("],\n");
  
    writer_->AddString("\"samples\":[");
    SerializeSamples();
    if (writer_->aborted()) return;
    writer_->AddString("],\n");
  
    writer_->AddString("\"locations\":[");
    SerializeLocations();
    if (writer_->aborted()) return;
    writer_->AddString("],\n");
  
    writer_->AddString("\"strings\":[");
    SerializeStrings();
    if (writer_->aborted()) return;
    writer_->AddCharacter(']');
    writer_->AddCharacter('}');
    writer_->Finalize();
  }
  
  
  int HeapSnapshotJSONSerializer::GetStringId(const char* s) {
    base::HashMap::Entry* cache_entry =
        strings_.LookupOrInsert(const_cast<char*>(s), StringHash(s));
    if (cache_entry->value == nullptr) {
      cache_entry->value = reinterpret_cast<void*>(next_string_id_++);
    }
    return static_cast<int>(reinterpret_cast<intptr_t>(cache_entry->value));
  }
  
  
  namespace {
  
  template<size_t size> struct ToUnsigned;
  
  template <>
  struct ToUnsigned<1> {
    using Type = uint8_t;
  };
  
  template<> struct ToUnsigned<4> {
    using Type = uint32_t;
  };
  
  template<> struct ToUnsigned<8> {
    using Type = uint64_t;
  };
  
  }  // namespace
  
  
  template<typename T>
  static int utoa_impl(T value, const Vector<char>& buffer, int buffer_pos) {
    STATIC_ASSERT(static_cast<T>(-1) > 0);  // Check that T is unsigned
    int number_of_digits = 0;
    T t = value;
    do {
      ++number_of_digits;
    } while (t /= 10);
  
    buffer_pos += number_of_digits;
    int result = buffer_pos;
    do {
      int last_digit = static_cast<int>(value % 10);
      buffer[--buffer_pos] = '0' + last_digit;
      value /= 10;
    } while (value);
    return result;
  }
  
  
  template<typename T>
  static int utoa(T value, const Vector<char>& buffer, int buffer_pos) {
    typename ToUnsigned<sizeof(value)>::Type unsigned_value = value;
    STATIC_ASSERT(sizeof(value) == sizeof(unsigned_value));
    return utoa_impl(unsigned_value, buffer, buffer_pos);
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeEdge(HeapGraphEdge* edge,
                                                 bool first_edge) {
    // The buffer needs space for 3 unsigned ints, 3 commas, \n and \0
    static const int kBufferSize =
        MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned * 3 + 3 + 2;  // NOLINT
    EmbeddedVector<char, kBufferSize> buffer;
    int edge_name_or_index = edge->type() == HeapGraphEdge::kElement
        || edge->type() == HeapGraphEdge::kHidden
        ? edge->index() : GetStringId(edge->name());
    int buffer_pos = 0;
    if (!first_edge) {
      buffer[buffer_pos++] = ',';
    }
    buffer_pos = utoa(edge->type(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(edge_name_or_index, buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(to_node_index(edge->to()), buffer, buffer_pos);
    buffer[buffer_pos++] = '\n';
    buffer[buffer_pos++] = '\0';
    writer_->AddString(buffer.begin());
  }
  
  void HeapSnapshotJSONSerializer::SerializeEdges() {
    std::vector<HeapGraphEdge*>& edges = snapshot_->children();
    for (size_t i = 0; i < edges.size(); ++i) {
      DCHECK(i == 0 ||
             edges[i - 1]->from()->index() <= edges[i]->from()->index());
      SerializeEdge(edges[i], i == 0);
      if (writer_->aborted()) return;
    }
  }
  
  void HeapSnapshotJSONSerializer::SerializeNode(const HeapEntry* entry) {
    // The buffer needs space for 5 unsigned ints, 1 size_t, 1 uint8_t, 7 commas,
    // \n and \0
    static const int kBufferSize =
        5 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned  // NOLINT
        + MaxDecimalDigitsIn<sizeof(size_t)>::kUnsigned      // NOLINT
        + MaxDecimalDigitsIn<sizeof(uint8_t)>::kUnsigned + 7 + 1 + 1;
    EmbeddedVector<char, kBufferSize> buffer;
    int buffer_pos = 0;
    if (to_node_index(entry) != 0) {
      buffer[buffer_pos++] = ',';
    }
    buffer_pos = utoa(entry->type(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(GetStringId(entry->name()), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(entry->id(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(entry->self_size(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(entry->children_count(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(entry->trace_node_id(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(entry->detachedness(), buffer, buffer_pos);
    buffer[buffer_pos++] = '\n';
    buffer[buffer_pos++] = '\0';
    writer_->AddString(buffer.begin());
  }
  
  void HeapSnapshotJSONSerializer::SerializeNodes() {
    const std::deque<HeapEntry>& entries = snapshot_->entries();
    for (const HeapEntry& entry : entries) {
      SerializeNode(&entry);
      if (writer_->aborted()) return;
    }
  }
  
  void HeapSnapshotJSONSerializer::SerializeSnapshot() {
    writer_->AddString("\"meta\":");
    // The object describing node serialization layout.
    // We use a set of macros to improve readability.
  
  // clang-format off
  #define JSON_A(s) "[" s "]"
  #define JSON_O(s) "{" s "}"
  #define JSON_S(s) "\"" s "\""
    writer_->AddString(JSON_O(
      JSON_S("node_fields") ":" JSON_A(
          JSON_S("type") ","
          JSON_S("name") ","
          JSON_S("id") ","
          JSON_S("self_size") ","
          JSON_S("edge_count") ","
          JSON_S("trace_node_id") ","
          JSON_S("detachedness")) ","
      JSON_S("node_types") ":" JSON_A(
          JSON_A(
              JSON_S("hidden") ","
              JSON_S("array") ","
              JSON_S("string") ","
              JSON_S("object") ","
              JSON_S("code") ","
              JSON_S("closure") ","
              JSON_S("regexp") ","
              JSON_S("number") ","
              JSON_S("native") ","
              JSON_S("synthetic") ","
              JSON_S("concatenated string") ","
              JSON_S("sliced string") ","
              JSON_S("symbol") ","
              JSON_S("bigint")) ","
          JSON_S("string") ","
          JSON_S("number") ","
          JSON_S("number") ","
          JSON_S("number") ","
          JSON_S("number") ","
          JSON_S("number")) ","
      JSON_S("edge_fields") ":" JSON_A(
          JSON_S("type") ","
          JSON_S("name_or_index") ","
          JSON_S("to_node")) ","
      JSON_S("edge_types") ":" JSON_A(
          JSON_A(
              JSON_S("context") ","
              JSON_S("element") ","
              JSON_S("property") ","
              JSON_S("internal") ","
              JSON_S("hidden") ","
              JSON_S("shortcut") ","
              JSON_S("weak")) ","
          JSON_S("string_or_number") ","
          JSON_S("node")) ","
      JSON_S("trace_function_info_fields") ":" JSON_A(
          JSON_S("function_id") ","
          JSON_S("name") ","
          JSON_S("script_name") ","
          JSON_S("script_id") ","
          JSON_S("line") ","
          JSON_S("column")) ","
      JSON_S("trace_node_fields") ":" JSON_A(
          JSON_S("id") ","
          JSON_S("function_info_index") ","
          JSON_S("count") ","
          JSON_S("size") ","
          JSON_S("children")) ","
      JSON_S("sample_fields") ":" JSON_A(
          JSON_S("timestamp_us") ","
          JSON_S("last_assigned_id")) ","
      JSON_S("location_fields") ":" JSON_A(
          JSON_S("object_index") ","
          JSON_S("script_id") ","
          JSON_S("line") ","
          JSON_S("column"))));
  // clang-format on
  #undef JSON_S
  #undef JSON_O
  #undef JSON_A
    writer_->AddString(",\"node_count\":");
    writer_->AddNumber(static_cast<unsigned>(snapshot_->entries().size()));
    writer_->AddString(",\"edge_count\":");
    writer_->AddNumber(static_cast<double>(snapshot_->edges().size()));
    writer_->AddString(",\"trace_function_count\":");
    uint32_t count = 0;
    AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
    if (tracker) {
      count = static_cast<uint32_t>(tracker->function_info_list().size());
    }
    writer_->AddNumber(count);
  }
  
  
  static void WriteUChar(OutputStreamWriter* w, unibrow::uchar u) {
    static const char hex_chars[] = "0123456789ABCDEF";
    w->AddString("\\u");
    w->AddCharacter(hex_chars[(u >> 12) & 0xF]);
    w->AddCharacter(hex_chars[(u >> 8) & 0xF]);
    w->AddCharacter(hex_chars[(u >> 4) & 0xF]);
    w->AddCharacter(hex_chars[u & 0xF]);
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeTraceTree() {
    AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
    if (!tracker) return;
    AllocationTraceTree* traces = tracker->trace_tree();
    SerializeTraceNode(traces->root());
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeTraceNode(AllocationTraceNode* node) {
    // The buffer needs space for 4 unsigned ints, 4 commas, [ and \0
    const int kBufferSize =
        4 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned  // NOLINT
        + 4 + 1 + 1;
    EmbeddedVector<char, kBufferSize> buffer;
    int buffer_pos = 0;
    buffer_pos = utoa(node->id(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(node->function_info_index(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(node->allocation_count(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(node->allocation_size(), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer[buffer_pos++] = '[';
    buffer[buffer_pos++] = '\0';
    writer_->AddString(buffer.begin());
  
    int i = 0;
    for (AllocationTraceNode* child : node->children()) {
      if (i++ > 0) {
        writer_->AddCharacter(',');
      }
      SerializeTraceNode(child);
    }
    writer_->AddCharacter(']');
  }
  
  
  // 0-based position is converted to 1-based during the serialization.
  static int SerializePosition(int position, const Vector<char>& buffer,
                               int buffer_pos) {
    if (position == -1) {
      buffer[buffer_pos++] = '0';
    } else {
      DCHECK_GE(position, 0);
      buffer_pos = utoa(static_cast<unsigned>(position + 1), buffer, buffer_pos);
    }
    return buffer_pos;
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeTraceNodeInfos() {
    AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
    if (!tracker) return;
    // The buffer needs space for 6 unsigned ints, 6 commas, \n and \0
    const int kBufferSize =
        6 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned  // NOLINT
        + 6 + 1 + 1;
    EmbeddedVector<char, kBufferSize> buffer;
    int i = 0;
    for (AllocationTracker::FunctionInfo* info : tracker->function_info_list()) {
      int buffer_pos = 0;
      if (i++ > 0) {
        buffer[buffer_pos++] = ',';
      }
      buffer_pos = utoa(info->function_id, buffer, buffer_pos);
      buffer[buffer_pos++] = ',';
      buffer_pos = utoa(GetStringId(info->name), buffer, buffer_pos);
      buffer[buffer_pos++] = ',';
      buffer_pos = utoa(GetStringId(info->script_name), buffer, buffer_pos);
      buffer[buffer_pos++] = ',';
      // The cast is safe because script id is a non-negative Smi.
      buffer_pos = utoa(static_cast<unsigned>(info->script_id), buffer,
          buffer_pos);
      buffer[buffer_pos++] = ',';
      buffer_pos = SerializePosition(info->line, buffer, buffer_pos);
      buffer[buffer_pos++] = ',';
      buffer_pos = SerializePosition(info->column, buffer, buffer_pos);
      buffer[buffer_pos++] = '\n';
      buffer[buffer_pos++] = '\0';
      writer_->AddString(buffer.begin());
    }
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeSamples() {
    const std::vector<HeapObjectsMap::TimeInterval>& samples =
        snapshot_->profiler()->heap_object_map()->samples();
    if (samples.empty()) return;
    base::TimeTicks start_time = samples[0].timestamp;
    // The buffer needs space for 2 unsigned ints, 2 commas, \n and \0
    const int kBufferSize = MaxDecimalDigitsIn<sizeof(
                                base::TimeDelta().InMicroseconds())>::kUnsigned +
                            MaxDecimalDigitsIn<sizeof(samples[0].id)>::kUnsigned +
                            2 + 1 + 1;
    EmbeddedVector<char, kBufferSize> buffer;
    int i = 0;
    for (const HeapObjectsMap::TimeInterval& sample : samples) {
      int buffer_pos = 0;
      if (i++ > 0) {
        buffer[buffer_pos++] = ',';
      }
      base::TimeDelta time_delta = sample.timestamp - start_time;
      buffer_pos = utoa(time_delta.InMicroseconds(), buffer, buffer_pos);
      buffer[buffer_pos++] = ',';
      buffer_pos = utoa(sample.last_assigned_id(), buffer, buffer_pos);
      buffer[buffer_pos++] = '\n';
      buffer[buffer_pos++] = '\0';
      writer_->AddString(buffer.begin());
    }
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeString(const unsigned char* s) {
    writer_->AddCharacter('\n');
    writer_->AddCharacter('\"');
    for ( ; *s != '\0'; ++s) {
      switch (*s) {
        case '\b':
          writer_->AddString("\\b");
          continue;
        case '\f':
          writer_->AddString("\\f");
          continue;
        case '\n':
          writer_->AddString("\\n");
          continue;
        case '\r':
          writer_->AddString("\\r");
          continue;
        case '\t':
          writer_->AddString("\\t");
          continue;
        case '\"':
        case '\\':
          writer_->AddCharacter('\\');
          writer_->AddCharacter(*s);
          continue;
        default:
          if (*s > 31 && *s < 128) {
            writer_->AddCharacter(*s);
          } else if (*s <= 31) {
            // Special character with no dedicated literal.
            WriteUChar(writer_, *s);
          } else {
            // Convert UTF-8 into \u UTF-16 literal.
            size_t length = 1, cursor = 0;
            for ( ; length <= 4 && *(s + length) != '\0'; ++length) { }
            unibrow::uchar c = unibrow::Utf8::CalculateValue(s, length, &cursor);
            if (c != unibrow::Utf8::kBadChar) {
              WriteUChar(writer_, c);
              DCHECK_NE(cursor, 0);
              s += cursor - 1;
            } else {
              writer_->AddCharacter('?');
            }
          }
      }
    }
    writer_->AddCharacter('\"');
  }
  
  
  void HeapSnapshotJSONSerializer::SerializeStrings() {
    ScopedVector<const unsigned char*> sorted_strings(
        strings_.occupancy() + 1);
    for (base::HashMap::Entry* entry = strings_.Start(); entry != nullptr;
         entry = strings_.Next(entry)) {
      int index = static_cast<int>(reinterpret_cast<uintptr_t>(entry->value));
      sorted_strings[index] = reinterpret_cast<const unsigned char*>(entry->key);
    }
    writer_->AddString("\"<dummy>\"");
    for (int i = 1; i < sorted_strings.length(); ++i) {
      writer_->AddCharacter(',');
      SerializeString(sorted_strings[i]);
      if (writer_->aborted()) return;
    }
  }
  
  void HeapSnapshotJSONSerializer::SerializeLocation(
      const SourceLocation& location) {
    // The buffer needs space for 4 unsigned ints, 3 commas, \n and \0
    static const int kBufferSize =
        MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned * 4 + 3 + 2;
    EmbeddedVector<char, kBufferSize> buffer;
    int buffer_pos = 0;
    buffer_pos = utoa(to_node_index(location.entry_index), buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(location.scriptId, buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(location.line, buffer, buffer_pos);
    buffer[buffer_pos++] = ',';
    buffer_pos = utoa(location.col, buffer, buffer_pos);
    buffer[buffer_pos++] = '\n';
    buffer[buffer_pos++] = '\0';
    writer_->AddString(buffer.begin());
  }
  
  void HeapSnapshotJSONSerializer::SerializeLocations() {
    const std::vector<SourceLocation>& locations = snapshot_->locations();
    for (size_t i = 0; i < locations.size(); i++) {
      if (i > 0) writer_->AddCharacter(',');
      SerializeLocation(locations[i]);
      if (writer_->aborted()) return;
    }
  }
  
  }  // namespace internal
  }  // namespace v8
  